Imaging: Forensic Photography

Imaging: Forensic Photography NP Marsh, Mayors Office for Policing and Crime, London, UK r 2016 Elsevier Ltd. All rights reserved.

Abstract This chapter looks at the use of digital cameras for evidential photography within the medical and forensic arenas. It briefly covers the day-to-day generic photographic issues such as composition and exposures, through to digital working practices, including camera choices and lenses and the terminology and technology such as sensor types and file structures. It also briefly looks at more specialists photographic applications for the recording of injuries or other latent evidence, such as cross-polarized illumination, reflected ultraviolet, and induced fluorescence. Finally it will look at the role of image production and digital storage and overall image quality.

Glossary Control or reference photographs These images are taken under the optimum lighting conditions and act as a control/reference image for any subsequent enhancement methods such as cross-polarized illumination. Forensic The application of scientific methods and techniques in the investigation of crime, relating to courts of law. Induced fluorescence Selected wavelengths of light are used to stimulate the surface of the subject, to induce fluorescence. This is done in subdued lighting conditions; any fluorescence produced is captured using a filtered camera. Infrared Uses wavelengths above 700 nm to photograph the subject. Images can only be recorded on an adapted camera sensitive to IR wavelengths.

Purpose In many forms of evidential casework, photography is used as a way to capture a scene, incident, or exhibit so that it can be viewed at a later date and gives an understanding of the original (Robinson, 2010). This means that any imaging device used, must be able to capture the scene in a way that can be replicated and understood.

Table 1

Pixel A pixel in a digital image a physical point in a raster image and is the smallest element of a picture represented on a screen that can be addressed by its coordinates. Reflected ultraviolet (RUV) A photographic process for recording images in the ultraviolet region of the spectrum only. Records an image using light of between 300 and 400 nm. This can only be undertaken on an adapted camera. White balance This important function, allows the correct setting of the white point within an image, so that it is not influenced by color variations caused by the illumination. Reducing the chances of an unwanted colorcast in the finished image. This can either be set in camera or during postproduction with some types of file structures.

However, in investigative casework this function becomes more complex, as the role of the image is often used for one of three main purposes, future reference, measurement and analysis, or communication (Table 1). It is therefore important when undertaking investigational photography that the photographer is aware of the intended use of the images. So that they can ensure they have the correct camera, lens, and lighting for

Purpose for photography

Reason

Future reference

Measurement and analysis

Communication

Purpose

Record for review by the investigator and court

A record of a sample that is suitable for certain analytical procedures

Objective

A representation that reminds one of the original situation

Accurate and rendered in a form suitable for specific analytical

A surrogate of a sample that helps another person visualize a key point being made by the investigator Shows key aspects of the original sample without evoking inappropriate emotional issues

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Encyclopedia of Forensic and Legal Medicine, Volume 3

doi:10.1016/B978-0-12-800034-2.00212-3

Imaging: Forensic Photography

the desired result, which will be bespoke for each case type.

Sensor Types Film the traditional medium of recording images, has now been replaced with digital for all evidential photography. However unlike film, which was uniform and came in a number of universal standard sizes, the three most common of which where 35 mm, 120 mm and 5  4 inches. Today's digital recording devices, not only come in various shapes, sizes, and recording quality, (Table 2) but there are also three main types of sensor. Two of these are in common use, whilst the third is limited to one manufacturer. There are also a limited number of other sensor types available, but are very specialist and not used in day-to-day evidential recording. The two commonest sensor types are: Charge-Coupled Devices

Charge-coupled devices (CCDs) sensors have been around for 30 years and are used in numerous cameras systems. In a CCD sensor, the light is converted into an electrical signal, and then every pixels electrical signal is funneled through a limited number of output nodes (often just one) where it is converted into voltage, buffered and sent from the sensor as an analog signal. Table 2

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This means that the entire pixel can be devoted to light capture and gives output uniformity, which is key to a high-quality image. These sensors tend to be used in high-end stills and video cameras and are generally more expensive to build than CMOS equivalents; they do however consume far more power to run than the CMOS sensor. Complementary Metal Oxide Semiconductor

The complementary metal oxide semiconductor (CMOS) sensor is probably the most common sensor in use and comes in a number of variations depending on manufacturer. The CMOS sensor is referred to as an active pixel sensor, where each pixel has its own charge to voltage converter, often including an amplifier, noise correction, and digitization circuits meaning the sensor outputs a digital signal. In the past this has meant that output uniformity from each pixel was much lower, but many of these issues have now been overcome. On the whole they are cheaper to manufacture and are now the norm for many professional, amateur, phone and web cameras. They also consume less power than many other sensor types. Both sensor types have advanced rapidly over the past few years and both have their advantages, although CMOS sensors have now gained dominance. It should be noted that both of the above are single flat layer arrays, which produce a gray scale response.

Digital stills recording

Description of device

Advantages

Disadvantages

Professional digital single lens reflex camera (DSLR) and high end amature DSLRs

High end camera with large file sizes, suitable for all types of evidential work Interchangeable lens Large selection of ISOs Full control over exposure Can shoot in all file formats Weather proof Mid-range amateur cameras with mediumsized files Reasonable priced Large selection of ISOs Full control over exposure Can normally shoot in a number of file formats Built in flash suitable for close range imaging Small and reasonable inexpensive Can normally shoot in a number of file formats

Expensive Requires a level of training and understanding Can require a separate flash unit

Amateur and compact DSLRs

Compact pocket cameras

Mobile phones

Small and to hand Images can be sent quickly Many have high-quality review screens

Lower resolution sensors Often have fixed non-changeable lenses, or limited zooms Can use batteries rapidly Limited flash

Fixed or limited lens choice Limited flash Limited file size May have focus limitation (e.g., poor macro) Can have poor battery consumption Small low-quality review screens Often low or interpilated resolution camera Limited flash Fixed lens or digital zoom May have focus limitations Limited file size

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To achieve color they are overlaid by a Bayer or mosaic mask, this is normally at a ratio of two green pixels for every blue and red one. The green pixel bias is to give the viewer an image, which our brain perceives as correctly color balanced. This is important to remember, as during photography and postproduction, some techniques may be recording using only one color. Therefore attention must be given to ensure that the area of interest fills the frame to ensure maximum use of the sensor. The third type of sensor is the ‘Foveon.’ Unlike the CMOS and CCDs, which only have one layer to respond to light, the Foveon sensor has three sensitive layers. One each for blue, green, and red; these layers are buried in silicon and take advantage that the light will penetrate downwards to the red layer at the bottom. This means not only can the Foveon sensor captures all three colors at once, but it also means that it has three pixels or photo detectors at each location, giving increased color saturation and image quality. This would appear to be the ideal sensor for evidential photographer, as it is a direct replacement for film. Unfortunately the Foveon chip is at present only used by the Sigma range of cameras. It is worth noting that camera sensors are always being upgraded or changed as technology is developed. Camera manufacturers have already increased the number and quality of pixels, on the sensor and even the dominance of the square pixel arrangement has been challenged in the past by Fujifilm, particularly with the launch of their Finepix S3, pro with its unique Hexagonal pixel. This hexagonal shaped pixel was interspaced with an ‘S’ pixel for normal exposures and a second one called the ‘R’ pixel giving excellent quality highlights. As mentioned above, there is another issue around sensors which the evidential photographer must be aware of and that is its physical size. Full size sensors are referred to as FX sensors and are 36 mm X 24 mm which is equivalent to the size of a 35 mm negative. These are used by both, Canon and Nikon in their professional range of cameras. However, for a number of reasons including cost, most manufacturers are producing a sensor, which is smaller than traditional 35 mm film at 25.1 mm  16.7 mm. These sensors are referred to as DX or Advanced Photo System-Classic (APS-C) sensors. The issue for the evidential photographer is that the size of the sensor alters the ‘standard’ focal length of the lens. The standard or normal lens has a focal length roughly equal to the diagonal across the image sensor plane and will give an angle of view, approximately equivalent to the perspective of the human eye. In FX sensors, this is accepted as being approximately 50 mm, whilst on a DX sensor this is accepted as being approximately 35 mm. In practice, this means, for example, if a 300 mm FX lens, is fitted to the smaller DX sensor, it will increase the magnification effect of the lens, by approximately  1.5

(depending on the make of DX sensor) giving you an approximate 450 mm lens. This can be advantageous in certain aspects of evidential photography, such as surveillance, where the longer focal lengths can be attained without the need for large lenses. If however this is reversed and a DX lens is placed on an FX sensor, the photographer runs a strong possibility of vignetting the image. This is when the light throw TTL, will not cover the whole surface of the sensor, leaving visibly dark corners or edges.

Capture Capability Not only do the sensors work in a different way to film and come in a number of sizes, they also have the flexibility to record the image information in a number of different formats. For the investigative photographer it is important to understand these formats, so as to work within forensically sound working practices (Table 3; Burdick, 1997). The main types of file are: RAW

A ‘raw’ file is the unprocessed or minimally processed data from the image sensor. A raw file format is proprietary to the manufacturer and the imaging system and may need to be converted to a nonproprietary format for viewing, editing, printing, etc. Proprietary software raw converters do not change the actual raw file, but apply the manufacturer's decoding when opening these files and similarly no changes are made to the file when editing: editing information is carried in an associated but separate file, i.e., image data remain unchanged. Raw files have a greater bit depth and greater dynamic range than other file formats. Raw files are essentially ‘digital negatives’ and the photographic industry standard. Various subsequent images and formats may be derived from the raw file, but the original is unaltered. Tagged Image File Format

Tagged image file format (TIFF) files are generally uncompressed, however the standard does allow for certain types of compression, although these are considered lossless (i.e., data may be discarded but no information is lost). TIFF files may be either 8-bit or 16-bit. When a TIFF file is edited any changes are embedded into the file, i.e., the image data is changed. These file are generally large as they represent the finished file. Joint Photographic Expert Group

Joint Photographic Expert Group (JPEG) files are compressed using lossy compression, which may result in the loss of relevant information. Generally, JPEG files are

Imaging: Forensic Photography

Table 3

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Digital terminology

CCD array CMOS Foveon

Pixel

PPI Megapixel

Bit Byte Megabytes (MB) Gigabytes (GB) DPI SD Micro SD CF Memory stick Smart media

Description

Uses

Charge-coupled device Complementary metal oxide semiconductor Three layer sensor recording RGB (red, green, and blue) separately on a different layer Is the smallest point in a raster image that can be controlled

The recording sensor used in most video camera and some digital cameras The recording sensor commonly used by many digital cameras

Pixels per inch Often used as a reference to the cameras resolving quality by manufacturers Basic unit of computing Unit of digital information Unit of measurement of digital information Measurement of digital information Dots per inch Secure digital memory card Micro secure digital memory card Compact flash memory card Memory card Memory card

CD DVD Blu-ray

Compact disk Digital versatile disk

Bit depth

Indicates the color of a single pixel

The recording sensor in some Sigma Cameras

In camera sensors each pixel contains a small cavity which collect the light photons, in many cameras these are between 4.5 and 7.2 mm where 1 mm is 1/ 1000 of a millimeter Used to describe the pixels per inch on a sensor or screen Generally the more pixels on the sensor the higher the quality of the final image. For example, a 3872 wide by 2592 high will be a 10.2 megapixels camera A bit or binary digit can only have one of two values 0 or 1 representing on and off Used in computing and telecommunications each byte consists of 8 bits 1 MB is 1 million bytes 1 gigabyte is 109 or 1 000 000 000 bytes Used in the printing process as a measurement of quality Used as a portable nonvolatile memory card in many cameras Used as a portable nonvolatile memory card in many phones A portable robust flash memory device used in most high-end cameras In portable memory device used in most Sony devices Smart media was aimed as being a replacement for floppy disks and contains a single NAND flash chip Used in many early electronic cameras and similar devices but is no longer manufactured Digital optical data storage device holding approximately 737 MB of data Digital optical storage device holding approximately 4.7 GB of information Digital optical storage device that can hold 25 GB on a single layer or 50.1 GB on a dual layer disk Bit depth indicates how many colors are available in images color palette in terms of the 0 or 1, which are used to specify each color For example Bits per channel Colors available Common name 1 2 monochrome 2 4 CGA 4 16 EGA 8 256 VGA 16 65 536 XGA, high color 32 16 777 216 48 281 trillion

8-bit color images, so any JPEG originating from a device with a higher bit depth will already be compressed by a reduction in dynamic range and bit depth. JPEG images may display characteristic ‘blocking’ artifacts as a result of the compression algorithm. There are 12-bit and ‘lossless’ options defined in the JPEG standard, however these not widely supported in products. JPEG 2000

JPEG 2000 is fundamentally different from JPEG, In that a different compression algorithm is employed, which has similarities to that of the Wavelet Scalar Quantization (WSQ) file format, which was specifically

designed for fingerprint images. JPEG 2000 is considered suitable for some evidential applications such as fingermark photography because it allows higher compression ratios with less perceptible artifacts. Each file format has its strengths and weaknesses. None of the formats need necessarily be avoided but it is important that the evidential photographer and those relying on images (particularly those at the end of the chain, the examiners) are aware of, potential weaknesses of certain file formats. For the purposes of producing a master copy of the image, it is recommended that all evidential files be initially shot and saved in the raw format. If raw is not an option TIFF is the next preference.

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Comparisons: Human Visual System versus Photography On the face of it, there would appear to be a number of similarities between the human visual system and digital stills capture, as we can see below: The eye has a pupil and the camera has an aperture. The eye has an iris and the camera has a shutter. The eye has a retina and the camera has a sensor. Both have lenses. The eye has a brain to process the image and the camera has image development software. The reality however is that our eyes are more like a video camera than a stills one, as they continuously change focus and react instantly to changes in brightness and color, building up an image in the brain. Whereas the digital camera, can only capture a still image, at any given moment in time, at a fixed point of focus. Thus any recording is limited by the exposure, lens, and illumination that are present at that time. Both systems operate to different standards, with our eyes relying on the brain to correct, interpret, and feedback what they are seeing, whereas a digital camera only sees the raw data for what it is. It is important therefore to ensure it is recording exactly what you require (Table 4).

Table 4

The Nature of Light Whilst a deep understanding of physics is not required to understand the key photographic issues some knowledge of the physical properties of light is desirable. Light is composed of small massless particles called photons. These travel in straight lines, unless their path is bent by reflection (as off a mirror), refraction (as in passing through a lens), or diffraction (as by passing close to the edge of an obstacle). The paths of these photons are called rays. Light can also be described by its electromagnetic wave. Each photon has a particular wavelength or frequency. Wavelength is what controls what is visually seen as color and its energy, which in turn it can impart to particles with which it might collide. Some of the measurements of light are key to taking photographs and are described in Table 5.

Taking Photographs The overall setup is as follows: 1. Ambient light is incident upon a scene containing the area of interest. 2. Some of this light is reflected off the elements within the scene and move toward the camera.

Comparison between human and photo visual process

Issue

Human vision

Photography

Focus and depth

Everything appears to be sharp and in focus

Dynamic range

Detail is resolved in both the highlight areas and deep shadow areas, giving a brightness range of about 1 million to 1 In photographic terms the eye can see approximately 24 stops of light difference

Only a limited portion of the image is in focus at any one time when the wide open aperture is open, when using at a small f/stop. Although this will vary depending on the aperture selected Digital cameras can only see at around 2000 to 1

Sharpness

Retinal image processing enhances edge detail, providing higher than expected sharpness

Color

The brain assigns colors names that we use to determine color which is based on the light wavelengths reaching the cones of the eye. Colors such as red are based on wavelengths whilst others such as brown which are mixtures have no physical wavelength basis The visual system can adapting a matter of seconds from very dark environments (tens of photons) to very bright ones (millions of photons) The brain has limited capacity to recall and enhance the signals it has received

Adaptation

Imaging postproduction

Top end digital cameras can see approximately 12 stops difference Lower end cameras can only see 5 stops difference All digital images require a degree of sharpness to be added but care must be taken to avoid creating artifacts, within image that can impair analyses and lead to misleading interpretations during communications with others The digital device applies colors based on its manufacturing parameters. There is the ability to adjust some of these settings as people to see reproduced colors differently, to natural colors due to the contextual interpretation differences Manual intervention is required to change a camera setting, in effect it is more akin to a video camera than as still one Digital post production allow the enhancement of any single pixel captured during an exposure allowing color, contrast, brightness, etc., to processed as required to give a finished product

Imaging: Forensic Photography

Table 5

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Description of common terms

Term

Description

Measurement

Photon basis

Luminous intensity

An indication of the brightness of a light source The brightness of a surface at a point The amount of light emitted into space Amount of light falling per unit area The amount of light reaching a sensor The unit of measurement for temperature

Candela (cd)

Total number of photon per unit time from a light source

Luminance Luminous flux luminance Exposure Kelvins

Table 6

Candela (m

2

)

Lumen (lm) Lux (lx) Lux seconds (lx s) Kelvins (K)

Photons per source Photons per source Photons per surface Photons per

unit time per unit of area on the surface of a unit emitted into a solid angle of space from a unit time per square meter on a receiving unit area on a receiving surface

Used to measure the colour temperature of light, daylight, and electronic flash are around 5500 K lower number are referred to warm colors and higher numbers are referred to as cool colors

Exposure terminology

Measure

Description

Controls

Focal length

The distance between the center of the lens and the point behind it where it forms an image of a distant object, usually measured in millimeters The opening through which light passes through the lens. Most lenses have an internal device called the diaphragm or iris which is adjustable normally the diameter of this opening is measured in millimeters A dimensionless number defined as the ratio of the focal length of the lens divided by its aperture. An indicator of the illumanace falling on the sensor for any lens no matter what its focal length A device within the camera that controls the exposure time

Image magnification per field of view

Aperture

f/stop

Shutter

ISO

Depth of field

A measurement of sensitivity of a sensor used in a camera. Defined by the International Standards Organization (ISO) and is proportional to the reciprocal amount of exposure needed to achieve a threshold of a sensor response. A setting of ISO 400 requires only half the light as a sensor at ISO 200 to achieve the same response and an ISO of 800 is twice as sensitive as ISO 400 The range of distances in front of the lens at which scene details re rendered sharply, this is adjusted by the f/stop setting

3. Some of this light passes through the camera lens. The amount of light hitting the sensor will depend on the aperture and the exposure time. 4. The lens will project a real image onto the image sensor. 5. The sensor will capture the light projected onto it via the array of pixels to form an image, which represent the original scene. The photographer must compose the field of view based around the requirements of the case. The exposure must then be determined, based upon the aperture, shutter speed, ISO, and the reflected light falling on the

Illuminate on the sensor surface for the given lens

Luminance on the sensor surface

The time that the light is hitting the sensor surface. It determines the range of relative movement speeds that can be ‘stopped’ Sensor sensitivity

Range of the subject to camera distances capable of sharp focus in front of and beyond the actual point of focus

subject. This is to ensure that the key features of the subject fall within the responsive portion of the sensors dynamic range. When there is insufficient ambient light the photographer will employ additional lighting such as electronic flash (Table 6). Most cameras have built in light meters and achieve this by measuring the ambient light passing through the lens. Separate exposure meters may be used in specific applications, such as when working exclusively with flash illumination, or when an incident light reading is required (light falling on the subject rather than reflected). In general most camera light meters are reliable and can accommodate a wide range photographic

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situations, including the use of TTL (through the lens) flash. The photographer can set the exposure meter for a number of scenarios either to concentrate on the overall frame content or portions of it (Blitzer and Jacobia, 2002). For example:

•

•

•

Spot metering where one small specific area of the viewpoint being measured. (This is normally positioned in the center of the viewfinder frame and is often highlighted, depending on the camera model.) Center weighted where the middle area of the viewpoint will be measured. (This is positioned in the center portion of the viewfinder frame and is often highlighted depending on the camera model.) Multiple points metering is where numerous points within the framed area will be measured automatically to give an average exposure for the whole image.

Instructions for the use of the camera light metering system and its combinations, are included in the camera manufacturers user manual. There are also situations where the photographer must fully override the automatic exposure and work in manual, such as ‘painting with light’ or low light photography. For many medical and forensic applications however one of three automatic exposure controls can generally be utilized, they are: 1. Program mode, here the camera automatically sets both the aperture and shutter speed. This is often the default setting on many lower end and phone cameras.* 2. Aperture priority mode, here the photographer chooses the desired aperture and the camera automatically selects the shutter speed. This mode is used when the subject's motion is not an issue and a good depth of field is required. For example, if the photographer requires a good depth of field where the foreground and the background are in focus they may chose a small aperture or large f/stop. Conversely if they want the subject in sharp focus but the background and foreground out of focus they may chose a large aperture and small f/stop. 3. Shutter priority modes, here the photographer chooses the shutter speed and the camera controls the aperture. Typically this is used, when the subject is moving and the photographer wishes to stop the action by using a fast shutter speed. Fast shutter speeds are also required when using telephoto lenses with the focal length acting as an indicator to the shutter speed. For example, the slowest shutter speed when handholding a 400 mm lens would be 1/400th. *

Reference should be made to the manufacturers handbook when using program mode, as in some cameras other functions such as image sharpening and color adjustments may be applied automatically to enhance the image, without the photographer being aware.

It should also be noted that when electronic flash is used, it will normally limit the shutter speed to 1/60th, although professional cameras may flash synchronize up to 1/500th or above. There are also a number of specialist techniques used within the medical and forensic environment that are worth highlighting. These are particularly used to record injuries or other evidence types, they are cross-polarized illumination, reflected ultraviolet (RUV), fluorescence, and infrared (Payne-James et al., 2012). It should be noted that before any of these are undertaken it is important that a reference or control is undertaken so that any differences can be seen and explained in context.

The Color Reference, or Control The reference or control photograph, is an image taken using daylight-balanced electronic flash, or using ambient lighting conditions and in many situations this may be the only image taken. Any injuries recorded must be clearly seen and if possible photographed at 901. Focus, exposure, and depth of field can be verified by checking the review screen on most cameras. They should also contain a scale and color checker if appropriate to ensure that the images are reproduced as faithfully as possible, by those responsible for printing. The use of brightly colored backgrounds should also be avoided as these can reflect color casts onto any item close to them. Ideally a gray cloth or a portable backdrop should be used and allows continuity between photographs (Gall, 2011).

Cross-Polarized Photography This technique takes the idea of singular polarization one-step further. As the name suggests this type of photography requires the light hitting the camera to be crosspolarized – this means the light has to pass through two polarizing filters at 901 to each other before reaching the camera sensor. The result is a color-saturated image, that shows little or no sheen/reflection on the skin and enhanced pigmentation, which in turn maximizes detail. This type of photography can be used for any of the following applications: bite-marks, burns, injury enhancement, implement marks, strangulation marks, general bruising, and gross specimen photography.

Reflected Ultraviolet This is a specialized technique and utilizes and area of the spectrum between 300 nm and 390 nm. At these wavelengths many substances absorb or reflect in a completely different way than they would under visible

Imaging: Forensic Photography

light. For example, melanin, the tanning agent of the skin, absorbs ultraviolet very strongly between 330 nm and 400 nm (other epidermal chromophores do not). Therefore any differences between pigmented and unpigmented skin are exaggerated by the application of these wavelengths. This technique is particularly useful for the visualization of old trauma injuries such as bites and burns. Additionally, RUV at this wavelength has virtually no penetration of the skin, so there is no scattering of the light. Because of this, it cannot be used to enhance bruising, but has the opposite effect of making it disappear. Thus this technique often used to enhance a trauma type injury by removing any visual secondary bruising. This lack of penetration into the skin also leads too much sharper images, meaning that surface damage is more easily seen. This technique can only be carried out using an adapted camera, as standard digital sensors, are protected by a filter to remove unwanted UV and infrared wavelengths from reaching the pixel layer of sensor.

Induced Fluorescence Induced fluorescence of injuries relies on the principle that many materials and substances, will fluoresce (glow) when illuminated by narrow bands of light, for example, ultraviolet. To assist in viewing this fluorescence and too remove unwanted wavelengths of light, the operator and camera must use a band pass filter which blocks the excitation wavelength, but allows the fluorescence to pass through. It is possible to exploit this phenomenon for the enhancement of injuries and many other types of forensic evidence. Depending on the subject, both flash and continuous excitation light sources can be used. No specialist adaptations to the camera are normally required, as any fluoresce seen will be within the sensitivity range of the camera sensor.

Infrared Infrared (IR) has long been used within medical environment because of two major benefits: first, it penetrates the superficial layers of the epidermis and reveals the structures beneath (Zharov et al., 2004) and second, the reflection and absorption characteristics of tissue in the IR differ from those in the visible spectrum. Venous blood absorbs IR heavily, whereas oxygenated blood reflects IR, thus vascular disorders such as varicose veins can clearly be seen. Although all digital sensors are by their very nature sensitive to IR up to around 1100 nm, to undertake photography you will require either infrared film or an adapted IR digital camera. Standard digital cameras cannot be used, as they contain a filter,

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which removes these IR wavelengths and stops them from reaching the sensor. If however the end image quality required is not high, then it is possible to use a video camera with a ‘night mode’ setting. This in effect removes the blocking filter from the optical path, allowing the sensor to record a gray scale image. Note any color associated with a viewed IR image, traditionally red or green, is false and is a software enhancement made to make the image look esthetically pleasing (Table 7).

Composition There are a number of guidelines, which should be followed when engaged in investigatory photography they are as follows (Redsicker, 1994): 1. Crop in camera. It is often that the case the significant aspect of the exhibit or scene is only contained within a small portion of the overall picture. Whilst it might be acceptable in an amateur image to crop at a later stage (thus reducing the size and quality of the image, if it is enlarged), it is not appropriate in a professional work. Accordingly the investigative photographer should be aware of the requirements of photograph and should frame the image accordingly, by either physically moving closer or further away from the subject, or by changing the lens so the area of interest fill the frame. If these images show very closely cropped areas, such as a bite mark, they should be augmented by positioning location photographs, which show the cropped area in relation to its surroundings. This is particularly relevant in the case of injury photography where areas of the body are easily transposed. Some amateur cameras use ‘digital’ zoom to fill the frame, this should be avoided, as unlike an optical zoom, which use the lens to optically enlarge the image on the sensor, digital zoom relies on cropping the sensor to achieve the magnification effect, in effect reducing the quality. Digital cameras also have finite resolving capability; this means that they can only resolve so many details across a frame. Therefore the full frame should be dedicated to the area of interest this will ensure that the highest quality image of image is preserved. The positioning or location photographs are exhibits that are used when communicating with others afterwards. 2. Use scales. In order to preserve the ability at a later time to make measurements or reproduce an image at a later date, it is important to place a reference scale within the image itself (Ferrucci et al., 2013). This should be positioned close to and on the same plane as the area of interest. There are a number of rulers specifically made for medical and forensic

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Table 7

Photographic techniques of note

Technique

Objective

Basic description

Painting with light

To record a scene in dim light

Macro photography

The close up photography of small items at 1:1 or larger The imaging of objects at magnification of greater than 1:1 Used to record images of substances, injuries, or other forensic evidence using specific band widths of light

The camera is placed on a tripod or fixed mount, open the shutter and walk around the scene lighting each area separately using either a handheld flash or other light source. When all the scene has been exposed close the shutter Use specialist macro lenses, bellows, or macro filters

Microphotography Alternative light source

Three-point lighting

Standard portrait studio lighting controls contrast, provides some shading on the subject, separating the subject from the background

Direct flash

A convenient method of illuminating a subject using either a built in or handheld flash pointed at the subject

Diffused direct lighting

This is used to soften harsh lighting associated with the direct flash Retains the flash on camera but reduces harsh shadows In close up work this reduces the sensitivity of surface roughness and produces even illumination

Bounce lighting flash Ring light

Copy lighting Perspective grid

A lighting arrangement to minimizes surface reflections Used to determine three dimensional information from scenes

Infrared (IR) photography

To see by the means of heat instead of visible light

Zone system

A process for determining exposure levels in order to maximize the impact of scenes dynamic range

Component panorama

A process of making a photographic representation of a very wide scene

Panoramic or 360 photography

A process of making a 3601 image of a scene

Generally the is achieved via attachment to a microscope Normally used to cause fluorescence in many substances, injuries and other forensic materials. Any fluorescence produced is at a longer wavelength than the excitation wavelength Some materials such as blood absorb certain wavelengths so this technique can be used to increase contrast Uses three lights. Two at the front on each side. One of which is generally at a lower intensity to create shadow form, the third light is raised above and is used to highlight the forehead and fill in the shadows A fourth light is sometime used behind and below the subject to separate them from the background Because the flash is generally built into the camera this produces a source of illumination at the same position as the camera. This means the front of the subject may be correctly illuminated but the other areas out of direct line of the flash illumination may be considerably darker A diffuser such as a translucent sheet made of plastic or cloth is placed over the flash head The flash is fired toward a wall, ceiling, or white card diffusing the light Utilizes a camera mounted unit which either encircles the front of the lens or positions small flash units around the lens The axis of two lights are set to 451 relative to the exhibits main surface and the camera is set at 901 to the surface A flat square of a known size is placed in the scene usually on the floor this is then used to extrapolate to vanishing points and establish a basis for making measurements. (this technique has been made largely redundant due to the use of laser scanners) Specialist films or digital sensors must be used that have sensitivity to the long wavelengths. Visible light is blocked and adjustments must be made to ensure sharp focus (some video camera fitted with ‘night mode’ have the ability to see IR. This physically removes the IR blocking filter from the optical path, allowing wavelengths of up to 1100 nm to reach the sensor) The brightness levels within a scene are categorized into zones. The exposure is then set to locate the key parts on the usable exposure range of the sensor Several images are taken at a different angle from the same viewpoint. Care must be taken that the images overlap to allow the image to be joined tog tether to create a single image A number of images are taken (dependant on the lens) from fixed position with the lens revolving around the no parallax point. This includes taking an imaging pointing straight up. These images are then stitched together to creates an equirectagluar image (the whole (Continued )

Imaging: Forensic Photography

Table 7

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Continued

Technique

Objective

Basic description

Bracketing

A means to help ensure getting a good exposure under conditions where it is difficult to measure

HDR

Allows scenes with a High Dynamic Rage to be imaged

Polarized light

A process to reduce surface glare

Cross-polarized light

A process to reduce surface glare

Telephotography

The capture of detailed images of distant objects using lenses of greater than twice the focal length of the standard lens A process for reducing harsh shadows or supplying supplementary illumination in underexposed areas

Fill in flash Off camera flash

A process of using a separate flash to illuminate a subject or area

Periphery photography

A process of recording the exterior of cylindrical object

Postproduction software

A process of postproduction for digital images

Stereo photography/3D photography

A means of showing depth in photography

purposes. Paper rulers, both sticky and non-sticky and standard plastic officer rules should be avoided. This is because they are known to stretch or have poor accuracy in the markings, which can be critical for some casework types (Payne-James, 2012). Some in addition to distance scales contain squares circles and color patches. It is good practice to keep several rulers on hand of varying sizes and some investigators take two photographs of key items one with the ruler one without. As a last resort and when a scale is not available, the use of known coinage can act as a

360 view appears flat, like a map of the globe in an atlas) this image can then be placed into software allowing it to be viewed as a true 360 view, so it would appear that the viewer is within the scene and can look up down or turn full circle Instead of one exposure being made, many are taken where the exposure is adjusted to over and under expose from the given exposure This uses the bracketing technique and then combines the images to produce an image that contains a full dynamic range allowing detail to be seen in both the highlights and shadows A polarizing filter is placed over the camera lens and rotated until the surface glare is minimized Two polarizers are used at 901 to each other, one is placed over the lens the other over the light source. The image captured should have no surface glare and should have increased color saturation. Often used for the enhanced visualization of injuries Requires telephoto lenses that have longer focal lengths than the standard lens. These cover only a small angle of view, with high magnifications of the subject A flash is used to partially illuminate an area of the scene that may have little or no illumination when other areas within the frame may be properly illuminated A normal flash unit is used attached to the camera via a lead or wireless link which allows the flash to be positioned wherever it is required. Often a number of units may be linked together to fire simultaneously Requires a specialist camera and is used to record fingermarks on cylindrical surface such as tins or cartridge cases. The images are taken in one exposure as the object rotates in front of the camera A number of software packages are available to handle the postproduction of digital images, typical processes are brightness, contrast, gamma, and color corrections. Many also contain an audit trail to show any changes made Uses either two cameras or one single camera with the two lenses. These lenses are slightly separated as are a persons eye Each image is shown to each eye separately at the same time via colored filters, polarizers, or stereo viewers. This produces the effect of depth within the image. More recently these images are processed via software and are viewed as three dimensional images on a computer screen

useful, but basic scale reference when placed next to the area of interest. 3. Keep perpendicular to the subject. In most investigative photos there is a key area, which the photographer wishes to capture. If the subject has a flat surface or a major dimension the camera should be held perpendicular to that surface or dimension. Ensuring this is done will greatly simplify subsequent measurements and analyses. In addition, the photographer should avoid extreme configurations that can complicate analysis. Examples of such

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configurations would include the use of very wideangle lenses (fisheye), very narrow angle lenses (long telephotos) and compositions that place the key subject near the edge of the frame rather than near the center. 4. The use of the standard lens for position shots or to depict accurate perspective, such as witness viewpoints. As already discussed, see manufactures handbook for guidance. Lenses with longer focal lengths (telephotos) than the standard lens will compress the distances by comparison to the standard lens and lenses with a shorter focal length (wide angles) will expand distances in comparison to the standard lens. 5. Subject failure. Over the years engineers have developed systems to take the guesswork out of photography including light meters, automatic exposure controllers, automatic printers image analysis and white point control, and autofocus to name but a few. However all of these assume that the photographer is dealing with a ‘normal’ scene. For the investigative photographer most scenes are quite different from vacation photography. For example, in a normal scene one can generally assume that the average reflection from the scene is close to that of a gray card that reflects 18% of the light. This is used within the camera to set the exposure correctly, it is also used to set the balance of the red, blue, and green components of light, or the basic coloration of the light source and balance it accordingly (white balance). It is also generally assumed that the main area of interest within the photograph shall be in the central position and that the rest of the image is background. If however the pathologist asks you to take a close up photograph of red (blood) wound on dark skin the scene would not be normal. The autofocus may or may not work, depending on the contrast within the mark and although the autoexposure may be fairly accurate, the white balance will be wrong and a manual adjustment will be required. The introduction of a gray ruler will help in the process and allow subsequent correction of the color balance during postproduction if required. Engineers regard the abnormal aspects of the scenes as ‘subject failure.’ It is therefore important that the investigative photographer knows when and how to correct for these abnormal situations and take steps to make manual overrides (Giorgianni and Madden, 1998). 6. It is also beneficial in many situations and particularly where multiple techniques are to be used, that a tripod is utilized. This ensures the continuity between images in regards to angles, distance, focus, and viewpoint. It also allows the use of slower shutter speeds, allowing the use of smaller apertures and greater depth of field.

Some of the appropriate techniques are listed in Table 6 and some postproduction images are listed in Table 8.

Image Processing Over the past decades photographers have developed a number of techniques to enhance and modify images in the darkroom to achieve the desired results (Reis, 2001). The developers of digital imaging software have now captured these functions using mathematical computer algorithms. This allows the photographer to apply these techniques with ease on a digital image and so it is important that the evidential photographer has a solid understanding of the possibilities. There are also protocols, which help facilitate legitimate image enhancement and avoid questionable image manipulation. Guidance on these are available from the Scientific Working Group on Imaging Technology (SWGIT) in the USA, or from the Center for Applied Science and Technology (CAST) in the UK and offer standard operating procedures (SOPs) covering a number of topics including audit trails, storage, and image handling. Best practice however is never to use the master image for image processing, but always a copy. This ensures that any changes are either visually apparent, or can be further analyzed by software. It is impossible to review all options within this chapter but a selection are given in Table 9.

Outputs At some stage the investigative photographer will be required to produce their images for third parties using one or more of a number of outputs. Hard-Copy

Although this is the traditional way to produce photographic images, it is rapidly losing ground to other types of digital medium. Digital images can be printed on a number of printer types including: Wet labs, these use a RGB laser to print onto traditional color paper which is chemically processed, they are generally high quality, fast, and economic to run. Inkjet printers, these are the most common type of printer with variable dot per inch (DPI) using a number of colored inks to build up the image normally Cyan, Magenta, Yellow, and Black (CMYK). High-end printers may use up to 9 inks to have a wider range of reproducible colors. These tend to be slow when printing at high resolution and may not be suitable for some types of evidential exhibits such as fingermarks.

Imaging: Forensic Photography

Table 8

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Image enhancement techniques

Type

Specific technique

Objective

Description

Size adjustment

Cropping

To create a new image of a different size

Cropping refers to removing parts of an unwanted image to concentrate on the area of interest Sizing refers to taking the existing image and either spreading it over a larger area or concentrating it down into a smaller one Interpolation is a process for accomplishing sizing with digital images, by adding or removing pixels In many imaging applications this function can be turned on and off. This is particularly relevant for evidential images Exporting is a variation of sizing and is used when the image is exported for other digital application such as the Internet, where a large file size may not be required Brightness changes the overall tonal range of an image while the contrast expands or shrinks the overall range within the image Gamma defines the relationship between a pixels numerical value and its actual luminance and translates how a camera sensor might see brightness in a linear relations system to the way the human visual system see it as a non linear function Curve adjustment tools allow one to apply different amounts adjustments to various portions of the tonal scale. The doge and burn tools allow these adjustment to be applied to a geometric area rather than the whole image Outlining involves drawing a line around the area of interest to be selected Similarity tools allow one to identify a small area and use it to define a basis for seeking similar areas Exclusion tools allow one to indentify a portion and then select everything else Once the area of interest is identified masking tools allow one to cover an area and then either process the area covered or no covered areas In color correction, colors within an image are changed to render colors of either familiar objects or of a color chart. Sometimes it is desirable to purposely change colors to highlight certain features of an image. Color corrections are also required when converting between RGB, CMYK, and lab color and to particular output devices such as printer, here the correct color profile should be assigned before exporting an image, to ensure it is replicated as seen on the original screen or viewing device There are a wide range of sharpening and diffusing software tools available but as a general rule they use they use changes in contrast along the edges. If this contrast is increased then edges appear sharper and if decreased they appear softer. These tools are useful up to a point but then there is a noticeable indication of image manipulation. (Continued )

Interpolation

Sizing

Exporting

Tone scale adjustment type adjustments

Brightness, contrast curve gamma, dodge and burn equalization

To change the visual output appearance of a single or multiple pixels in an image

Selection

Similarity outline, exclusion, masking

To define areas of an image that will be subjected to further processing

Color adjustment

Correction change copying

To change the coloration of either the full or parts of an image

Edge adjustments

Sharpening blurring

To render the edges of object in an image either more clearly or more diffuse

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Table 8

Continued

Type

Specific technique

Objective

Description

Defect removal

Cloning, redeye, despeckle, writing, and airbrush

To correct for know accidental image defects, such as dust spots and redeye effect

Frequency filtering

Fourier, spectral, and others

To accentuate or remove patterns from an image

Color filtering

Multispectral imaging

To accentuate and separate colors from within an image

Area and shape adjustments

Transforms perspective

Enhancement

Various

Changes the apparent shape of an object within an image. These tools can be used to change perspective To visually alter the image to present it for its purpose

Manipulation

Various

To visually alter an image

Dye sublimation This use heat to transfer the dye to the paper, these printers use Cyan, Magenta, Yellow, and Overcoating (CMYO) and are supplied as a cartridge ribbon. Unlike the CMYK as used in the above printers, black is replaced by a clear overcoat which seals the image from UV light and moisture. These printers generally have a good tonal range but again tend to be slow and have a high cost per print.

Also it is not possible to reconstruct what was not there in the first place Redeye, despeckling are localized tools less inclined to support gross alterations. Redeye as its name suggests removes the red reflections caused when the open pupil of the eye reflects a photographic flash. Writing involves the direct addition of text information to an image, that was not part of the original photograph. It should only be used with a clear need and description An image is nothing but a series of changes in brightness over a space on a surface. They can be represented by a sum of the sine and cosine waves of brightness with distance. In this way all mathematical based frequency filtering techniques can be used selectively to enhance or remove patterns from an image. However the use of such techniques on images such as fingermarks may also remove part of the mark, so must be used with caution Multispectral imaging allows an area to be captured and then separated into its color components. Often used to remove colored fingermarks from a patterned background. Unlike the Fourier technique, this means that marks across a patterned surface will not lose detail and will remain as a color The area of the image to be required is selected and the tool is applied. These tools use basic geometric rules and interpolation as need to complete local resizing The general enhancement of an image allows the use of tools listed above along with color, gamma, brightness, contrast, etc. These are all used to ensure that the final image shows what the photographer wishes it to present. For example, a scene would be enhanced so that it replicated the brightness and color balance of the original scene. A fingermark may however be enhanced to increase contrast and to remove the color element leaving a grayscale, to improve the visual quality of the final image Manipulation is generally seen as a negative terms within evidential imaging. It suggests that an image has been manipulated to achieve a result that may be deceiving to the viewer. Although in reality it just refers to manipulating the pixels of the image

Each of the above will use different color profiles for their paper and ink. The photographer must be aware of these profiles when sending an image to print, so that the final image contains the correct color balance. Failure to do so will give the final print a colorcast which will mean that it no longer offers a true representation of the original. For example, a brown jumper seen on the camera review screen may appear

Imaging: Forensic Photography

Table 9

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Digital printers

Type

Modes

Description

Pros and cons

Inkjet

Paper transparency

Small drops of ink are applied to the surface of a receiver sheet

Inexpensive although the inks can be moderately expensive. Can write to a number of paper surface finishes Does not make high-quality transparencies due to the inks scattering light. Printer tend to be slow and image stability can vary

Several such drops are required to render an image. In color images these drops will be made from a number of colored inks

Dye sublimation

Paper transparency

Photographic paper

Paper transparency

Dye is fumed of a ribbon an heat bonded to the surface of the receiver sheet. The amount of dye applied in each location can be adjusted so that the dots and pixels are the same Lasers are used to expose regular photographic paper usually in the form of a mini lab paper processor

orange when printed, if the color profile is not adjusted (Table 9). Projection and Screens

Increasingly in both the US and UK investigators are making use of computer presentations to deliver evidence, in addition to, or sometimes as the replacement for traditional prints. This has the advantage that all the members of the court are reviewing the same image at the same time. The key factors in choosing a projector screen or other digital device are brightness, resolution, and contrast ratio. Common today are projectors and screens with 1500 lm or more and contrast ratios of up to 5000:1. Most monitor or television screens will run in high definition (HD) at 1920  1080p, whilst most mobile tablets displays run at around 768  1024. Other mobile devices such as phones will run at much lower display qualities so you will need to check the manufactures guidance. These devices are continually developing and advancing in quality, it is therefore important that the photographer is aware of the end requirement, as a different file sizes are required for each. For example, to achieve a full screen image on a large HD screen, will require a larger file with more pixels, than to display it on a mobile phone. Data Storage

In traditional film photography, the film itself was the storage medium and to ensure longevity it was kept in cool, dry, and dark conditions. The storage of digital images involves a different set of criteria including file formats, storage medium, and filing systems.

May not be suitable for some types of evidential work such as fingerprints These devices are expensive as are the materials. However they make high-quality prints and transparencies. The printing speeds are relatively high and the dye stability is good. Suitable for all types of evidential image These are expensive devices but price per print is relatively cheap. Printing speed can be fast and the image quality is very high image stability is good and often archival quality suitable for all types of evidential image

Digital images reside in computer files and these files must adhere to a strict file format for them to be readable in the future. Due to the nature of digital cameras, these files can be large and quickly consume space. Therefore the end usage of your image may dictate the file format of choice. For example, if you still require continuity with the original image, then you may save the 20Mb RAW file. If however the image is only for the Internet, then it is possible to reduce the redundant information by the use of compression. Because of the large file sizes it is possible to reduce the redundant information by the use of compression. If this is done without losing any essential information, the process is ‘lossless compression. On average this is normally in the realms of 2:1, thus 18 million megabytes (18 Mb) can be reduced to 9 million without the loss of information. When the file is opened to show the original image, all the information will remain intact. This is possible to do in some cameras, as a raw file or as a TIFF file in postproduction. In addition to lossless compression, there are also ‘lossy compression’ methods; these utilize complex mathematical relationships and are able to selectively to eliminate information that is unlikely to be important to substance of the image. The commonest method is JPEG conversion and has the advantage that the compression ration is variable with the operator adjusting the compression ration required. It is important to note that the higher the compression rate the greater the chances of lost information. In addition to losing information, high ratios of compression can create artifacts within the image and again the greater the compression the greater the number of artifacts. Modest levels of JPEG compression of ratios of approximately 5:1 are generally accepted as being satisfactory.

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For evidential photographers the correct choice of file structure is vital, guidance has been laid out by SWGIT and CAST in their guidelines. SWGIT break this down into category 1 and category 2 images. Category one images are those that are used for overviews or scene setting, whereas category 2 images are used for analyses or accurate reproduction. For example, an evidential photographer would not compress an image of a fingermark, in case the compression process altered the detail within that mark. Whereas they may compress the file for a motor vehicle, in which loss of detail may not be critical (Table 10). Once the format issue has been resolved, one needs to choose a medium for storage. Some systems rely on servers that are backed up and protected as a means of archival storage. Others write files to be archived to stable write once medium such as write once, read many (WORM) CDs, DVDs or Blue-ray disks. The server approach is convenient for the end user and if properly maintained is quite satisfactory. It has a downside, in that forensic casework material must be kept for decades and although there is a very low likelihood of calling the material back after the first few years. This results in large amounts of storage space dedicated to images that may never be retrieved. The utilization of separate CDs, DVDs or Blue-ray disks on the other hand provides reliable long term storage which can be updated as technology moves forwards.

Image Quality Unlike vocational or recreational photography, evidential photography must be reliable in the eyes of the

Table 10

judicial process. To achieve this we must rely heavily on two components of the image: 1. The actual composition of the image, does it in fact show what we want it to show and if so, can it be easily understandable by a third party. 2. The type of file and file size we shoot. If we look at composition first we have already seen that it is important to ensure that the area of interest fill the frame and superfluous areas are cropped out so they are not distracting. We have also seen that on many occasion extra lighting may be required often in the form of flash or other alternative light sources. There are also other factors, which may not be so obvious that may also need to be considered, such as the focal length of the lens. For example, to show a scene from the perspective of an eyewitness a standard lens must be used (dependent on the sensor in the camera). As a lens with a shorter focal length, will appear to make the subject further away than it is. Alternatively using a longer focal length lens than the standard will appear to make the subject closer than it is. Both of these would produce misleading images and would not be a true reflection of the original scene from the eyewitness point of view and would therefore inadvertently deceive any investigation or possible judicial proceedings. It is also important to remember what the end product is to be used for. If the image is recreational and is just to be shown on the Internet, at screen resolution than it might be acceptable to shoot a small file. However for evidential photography it is nearly always best practice to shot in the highest quality setting you have. On most reasonably priced cameras this is the raw file. As already discussed these files are as the sensor sees the image ‘the

Common file formats

Format

Type

Compression

Comments

RAW

NC

None

Tiff

NC

None

LZW

LLC

2:1

JPEG

LC4VLC

2:1

JPEG 2000

LC

o100:1

BMP/Bitmap image files

NC

Raw images files contain the minimally processed data from the image sensor of either a digital camera image scanner, or film scanner. Raw files are named so because they are not yet processed and are therefore not yet ready to be printed or edited A robust and widely used format that does not compress the image, often used for archiving a finished image A widespread file format that uses standard TIFF format but add losses compression A widespread file format of compression which can be adjusted by the users at lower levels of compression It is almost impossible to detect the losses as the compression is increased the losses increase and can become quite noticeable. At compressions rate of more than 10:1, it is also possible to see artifacts in the images Jpeg 2000 uses wavelet compression allowing high compression rates to be used without loss of image quality however it is not widely used within the evidential arena BMP files is a raster image file format used to store bitmap digital images independent of the display device especially on Microsoft windows

Abbreviations: LC, lossy compression; LLC, lossless compression; NC, no compression; VLC, visually lossless compression.

Imaging: Forensic Photography

digital negative’ unfortunately this format is often overlooked, because it cannot be viewed without bespoke software, unlike a jpeg that is viewable on any computer system. However as an evidential photographer we are not looking at speed but quality and once captured in raw, you have access to the full 12 or 14 bit color and dynamic range of the image, giving 4096–16 384 shades per channel, allowing accurate and subtle adjustments to the image quality. This is unlike a jpeg 8 bit image where only 256 shades per channel are available. The other issue, which is often overlooked, is around the quality or resolution of image required for certain categories of work. For example, some evidential images such as fingermarks must be shot at prescribed ppi which in the case of fingermarks is either 1000 or 500 ppi (see SWIGIT and CAST guidance). This means that you must position your camera at a distance that will render that resolution or greater on the camera sensor. For example, to achieve a capture of 1000 ppi, a camera with a sensor of 3872  2592 such as a Nikon D80 could only cover an area of approximately 3.8  2.5 in. Whilst the Nikon D800 could achieve the same resolution over an area almost twice as big of approximately 7.3  4.9 in. Evidential images such as finger and shoe marks, should never be rescaled too artificial recreate these resolutions from inferior resolutions, as the process is likely to introduce unwanted artifacts.

Summary and Conclusion Digital technology has significantly impacted on all aspects of evidential photography including forensic and medical work. These developments will not stop and will greatly expand the capabilities of the investigator to document and analyze evidential material. It is therefore vital that the original image is captured at the highest possible quality in the right format and then processed in accordance within an operating procedure that allows it to be viewed, or reproduced in a way that allows it to be of evidential value. Fortunately there are groups such as SWGIT and CAST that are working to evaluate and give guidance in terms of working practices and training and many of the above issue have recently been investigated by the Dermatological Patterned Injury and Capture Analysis, research group (DePICA). This research group comprises multiprofessional collaborators from a wide range of backgrounds including the Metropolitan Police Service (MPS), the Home Office Centre for Applied Science and Technology (CAST), the National Injuries Database at the National Crime Agency (NCA), Barts and the London School of Medicine and Dentistry, Expert Forensics Ltd, and Cardiff University Schools of Medicine, Dentistry, and Mathematics. It has two main research aims: (1) to assess current image capture methods and practices and (2) to produce guidelines for best

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practice, which looked at how images where being captured within forensic/medical environments with the hope of giving national guidance (within the UK). There are similar efforts in other countries and these can be found through national police forces. In addition there are specialized organizations such as the Institute for Forensic Imaging, as well as numerous books and web publications supporting this evolution.

References Blitzer, H., Jacobia, J., 2002. Forensic Digital Imaging and Photography. London: Academic Press. Burdick, H., 1997. Digital Imaging Theory and Applications. New York, NY: McGraw-Hill. Ferrucci, M., Doiron, T.D., Thompson, R., et al., 2013. Dimensional Review of Scales for Forensic Photography Document’ 243213. US Department of Justice Award Number 2010-DN-R-7121. Gall, J., 2011. Current Practices in Forensic Medicine, first ed. UK: Wiley-Blackwell. Giorgianni, E., Madden, T., 1998. Digital Color Management. Reading, MA: Addison Wesley. Payne-James, J.J., 2012. Rulers and Scales used in measurement in forensic setting: Measured and found wanting!. Forensic Science, Medicine, and Pathology 8 (4), 482–483. Payne-James, J.J., Hawkins, C., Baylis, S., Nicholas, P.M., 2012. Quality of photographic images provided for injury interpretation: Room for improvement? Forensic Science, Medicine and Pathology 8 (4), 447–450. Redsicker, D., 1994. The Practical Methodology of Forensic Photography. Boca Raton, FL: CRC Press. Reis, G., 2001. Photoshop CS3 for Forensic Professionals. New York: CRC Press. ISBN 978-0-470-11454-4. Robinson, E.M., 2010. Crime Scene Photography, second ed. Indianapolis, IN: Wiley Publishing Inc. Zharov, V.P., Ferguson, S., Eidt, J.F., Paul, C., 2004. Infrared Imaging of Subcutaneous Veins. doi:1002/lsm.10248.

Further Reading Ferrucci, E., Madden, T., Thompson, R., et al., 1998. Digital Colour Management. Boston, MA: Addison Wesley. Giorgianni, E., Madden, T., 1998. Digital Color Management. Reading, MA: Addison Wesley. Hinkle, D., 1990. Mug Shots. Boulder, CO: Paladin Press. Jacobson, R., Ray, S., Attridge, G., Axford, N., 2000. The Manual of Photography, eighth ed. Oxford: Focal Press. Langford, M., 1985. Advanced Photography, fifth ed. Oxford: Focal Press. Langford, M., 2013. Langfords Advanced Photography, The Guide for Aspiring Photographers, eighth ed. Burlington, MA: Focal Press. Meyer-Arendt, J., 1995. Introduction to Classical and Modern Optics, fourth ed. Englewood Cliffs, NJ: Prentice Hall. Miller, L., 1998. Police Photography, fourth ed. Cincinnati, OH: Anderson. Pedrotti, F., Pedrotti, L., 1993. Introduction to Optics, second ed. Upper Saddle River, NJ: Prentice Hall. Russ, J., 1995. The Image Processing Handbook, second ed. Boca Raton, FL: CRC Press. Russ, J., 2001. Forensic Uses of Digital Imaging. Boca Raton, FL: CRC Press.

Relevant Websites www.cannon.com Canon. www.cast.org CAST: Center for Applied Special Technology. www.fujifilm.com Fujifilm.

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http://idps.org.uk/RawvJpeg.pdf Ipswich and District Photographic Society. RAW, JPEG and TIFF. www.Nikon.com Nikon.

https://www.swgit.org Scientific Working Group on Imaging Technology. www.sigmaphoto.com/cameras Sigma Cameras.