A series of footwear marks are found in soil and the chosen method of recovery is photography. Using the recommended procedure, delivered in Week 3, give technical descriptions of, for example, Depth of Field, Perspective error, Resolution etc.
Crime scene photography is focused on taking accurate images of crime scenes and criminal evidence, so that these images can be used in a criminal investigation, and in the potential prosecution for criminal activities. People have been taking photographs of crime scenes ever since the first camera was invented because it was realised that still images could be a useful tool in the process of a criminal investigation. Modern photography of a crime scene is intended to provide a detailed, accurate and truthful image of the scene and to accurately document both the crime scene itself and the ensuing criminal investigation. Crime scene photographers are the first people allowed into a scene of crime, this is to try and maintain the crime scene and provide as truthful image as possible. Crime scene photographers start by taking overall scene shots and then move into smaller areas and then take specific shots of potentially important evidence such as footwear marks. The images taken by a crime scene photographer must contain evidence markers and scales, and rulers when necessary to retain relevance to the investigation. Police officers may use images from crime scene photography to be able to reconstruct a crime scene. The photos may also be used in interrogation and in courtrooms to provide both the judge and the jury with evidence of what the scene looked like and of important features of a crime scene, for example a knife. It is also a lot easier and safer to show the knife, which could be a murder weapon, as an image to the courtroom along with the correct documentation in which the evidence pathway and handling of the evidence document, rather than bringing the actual evidence package into the courtroom. Digital cameras have massively expanded the field of photography in a criminal investigation; this is because they allow photographers to shoot images extensively, allowing them to capture every possible detail on a small media card rather than rolls and rolls of film. However this could also provide problems because it could lead to a photographer or even an investigator flicking through hundreds, or thousands of images of a single crime scene. Although this method provides better probability that a potentially important image may not be missed because of a crime scene photographer being conservative with the camera and amount of film used.
When entering a crime scene the photographer will take images from a long range that show the overall crime scene, mid-range photographs will be taken that show a closer view of a certain area; and close range photographs will concentrate on a particular area or object such as a footwear mark or impression. Crime scene photography is a non-destructive method of recovery of a footwear mark. Photography of a footwear mark should always be the first method of recovery by a crime scene investigator before any other recovery methods are used. Most close range photographs will be captured at less than actual size; this will mean a rigid scale will need to be included. When enlargements are made to an image to examine certain aspects of that image, they can be enlarged to a natural size only by referring to that scale. This means that the enlargement is sized so that for example 1mm on the scale in the enlarged photograph equals one actual millimetre. A camera which would produce an image which is the natural size image (a 1:1 photograph) is not practical to be present at a crime scene, the use of a practical scale in the photograph is absolutely essential so the photograph can be accurately enlarged. The scale used should ideally extend the full length of the impression, it should be positioned evenly and on the same plane as the impressed surface, this is more difficult with a short scale. The length of the scale is important when making natural sized prints of the image for accuracy purposes.
The scale should be level and parallel to the footwear impression, this is because if the scale is not level and parallel, it can cause perspective and scaling problems. Images taken of impressions from directly above the impression and taken in the correct manner will not provide significant perspective problems. Something present in the image will provide viewers of an image, such as the judge or the jury, confirmation that the perspective is correct. Whereas pronounced perspective problems are usually very clear in a photographed impression, minor perspective problems are harder to identify without aids. In the case of a ruler, certain aids can provide support in detecting and potentially correcting perspective problems. A right-angled ruler is a better instrument to determine and correct any perspective problems than a straight ruler. Right angled rulers are also very helpful when a photographer is forced to take an image of a footwear impression from an angle as it is easier to correct any perspective problems. When using a right angled ruler it is important that the ruler is level, as an angled or tilted ruler could make the photographed impression appear out of perspective. The scale should conform to both length (1st dimension) and width (2nd dimension)1. When photographing three dimensional footwear impressions, it is essential that the depth of the impression is measured in its entirety. To do this several photographs have to be taken with the scale positioned at numerous different depths.
The numerous photos taken are to be taken from the same position with the scale square to the lens at all times and it moves further and further away from the lens to show the different depths of the impression. In an image of a footwear impression several things should be included in the image for it to be helpful to an investigation and to provide as much information as possible. These items include an identification label, an orientation arrow, and an angle setter. The identification label must always be included and the label should tell the image viewer the location of offence, location of the footwear mark, the date, the crime scene investigator’s name and the exhibit number. This is important because at a crime scene there may be several footwear impressions maybe at different locations throughout the crime scene, having the identification label in each image enables each image to be linked to other details such as scene sketches, notes, logs as well as lifts and casts. The orientation arrow should be placed within the photographic image. This enables the orientation of the footwear mark to be determined within the scene. The angle setter is a spirit level that determines the angle at which a footwear mark lies within a crime scene.
The use of the angle setter will help the photographer ensure that the correct procedures have been adhered to regarding the capture plane, scale, label and footwear mark are on the same plane. The tripod is an important factor when photographing footwear marks. The ideal position for a footwear impression image is directly above the impression. The tripod helps with the proper positioning of the camera as a tripod can hold the camera directly below its’ centre and provides a steady base which helps hold focus and prevent movements of the camera affecting the image. In order to avoid a perspective problem it is important that the camera is parallel to the footwear mark, and the tripod is able to provide this even if the footwear mark is on an angle which would be shown on the angle setter. When using a tripod it enables the camera timer to be used also to minimise movement of the camera, by reducing the movement put upon the camera when the capture button is pressed, which may also cause a loss of focus or a perspective problem. The tripod also enables the photographer to have his hands free for other tasks such as managing the light source and exposure. A tripod also makes it easier when photographing multiple footwear marks or impressions as it makes it easier to move from one place to another within a crime scene. To ensure everything is correct with an image before the matters of exposure and lighting are dealt with, the photographer can use a cameras’ viewfinder to ensure that angles, image size and focus are all correct before attempting to set the lighting and exposure. When photographing three dimensional footwear impressions a cameras aperture should accommodate the depth of the footwear mark. The NPIA recommend an aperture setting of between F16 & F22.
For two dimensional footwear marks the NPIA recommend an aperture setting of around F8 to F11. There are many different types of lighting that could be used by a photographer at a crime scene. When photographing footwear marks and impressions. Some marks and impressions can be taken using natural light, or sometimes natural light has to be restricted; however more often than not artificial lighting will have to be used. The purpose of lighting is to achieve a contrast between a footwear mark and the soil or other surface the mark or impression lies in or upon. If natural light does not suffice to provide the image with enough contrast there are many artificial light sources that could be used by the photographer such as, reflectors, crime lights, slide projector, oblique LED’s or fibre-optics, polarised light, or sometimes a camera flash can provide the needed contrast in the image. However when using a camera flash the flash should never be mounted on the camera, this is because a flash mounted on the camera causes a reflection of light back into the lens, known as “flash-bounce”2 and this flash bounce causes a section of the photograph to become over-exposed and will be of no use in the investigation.
This image shows a footwear mark with over exposed areas, these over exposed can be seen around the top end of the heel area of the shoe where there is little detail as a result of over exposure.
This image shows the footwear impression in the soil, however there is no lighting sources to provide contrast and detail within the footwear impression. Oblique lighting allows maximum detail to be captured by the photographer by providing contrast. To obtain this a light source has to be placed at a low angle of incidence relative to the surface the footwear impression is in. This low angle creates shadowing within the footwear marks higher and lower areas and this provides the increased amount of contrast within the image. For this impression in the soil, the angle of incidence to place the oblique lighting source depends on the depth of the footwear impression. The greater depth of the impression, the greater the angle of incidence will be, therefore if a footwear mark is deep the oblique light source will be higher from the ground. When using oblique lighting several images have to be taken of the footwear impression and for each image the oblique light source has to be repositioned.
The idea of oblique lighting is to improve the contrast within an image by creating shadows on the low areas while illuminating the higher areas. When photographing the footwear mark as a photographer they test different light sources to find the best possible image, although the photographer always has to have the inverse square law3 in mind. The inverse square law states that an object twice the distance from a source of light will receive a quarter of the illumination. In terms of footwear marks basically it means that if the oblique lighting source is positioned along the length of the footwear from the toe end of the footwear mark, the toe end may be over exposed and the heel end under exposed. A method called fill lighting4 can counteract the under exposure. This uses a reflective surface placed at the opposite end of the footmark to the oblique lighting source, this reflects some of the oblique lighting back into the footwear mark to try to create more contrast and therefore more detail within the image.
From a photographer’s perspective the inverse square law means that if you double the distance of the footwear mark from the light source, you will need four times the amount of light for the same exposure. Perspective problems occur when the camera is not parallel to the footwear mark or impression that is being photographed. To avoid this problem a tripod should be used and the image should not be taken by hand. Although in three-dimensional footwear impressions, sometimes even if the camera is parallel to the impression perspective errors can occur commonly in deep impressions. This occurs because in producing the image, the impression is converted from a three dimensional impression to a two dimensional image of the impression. The National Policing Improvement Agency (NPIA) provides a 14 point guideline for taking a footwear image. These read : “1. Handhold the camera to determine the tripod position, image size and access.
2. Place grey ridged ‘L’ scale alongside footwear mark so it conforms to length and width.
3. Ensure ‘L’ scale is on the same plane as the footwear mark.
4. For three dimensional footwear marks a series of photographs will need to be taken with the ‘L’ scale at the various depths and angles, which represent all the depths and angles of the footwear mark.
5. Include directional arrows on the label.
6. Install the tripod and camera – ensure everything is stable. 7. Align the camera, footwear mark and scale accurately using the angle setter. 8. Set the camera so the footwear image is as large as possible in the view finder and within the printing parameters. 9. Select an aperture with appropriate depth of field.
10. Select appropriate lighting or shading.
11. For two dimensional footwear marks consider the use of reflectors to obtain a more even distribution of light across the footwear mark. 12. Consider restricting any ambient light (natural or artificial) falling onto the footwear mark area in order to achieve the best effect of oblique light. 13. Work out exposure time to suit aperture and lighting selected. 14. Take several photographs, change position of the source of light to ensure that all areas of the footwear mark are correctly exposed.”5
This is my image of the footwear impression in soil.
These guidelines will offer the correct method leading to a high quality image that can be relied upon in a criminal investigation. In conclusion the photographer has to take responsibility in regards to the accuracy and care taken when shooting the images and this will lead to high quality images of footwear impressions.
