Forensic photography


Forensic photography, also referred to as crime scene photography, is an activity that records the initial appearance of the crime scene and physical evidence, in order to provide a permanent record for the courts. Crime scene photography differs from other variations of photography because crime scene photographers usually have a very specific purpose for capturing each image.
Crime scenes can be major sources of physical evidence that is used to associate or link suspects to scenes, victims to scenes, and suspects to victims. This is Locard's exchange principle. It is the basic tenet of why crime scenes should be investigated. Anything found at a crime scene can be physical evidence. In scientific crime scene investigation, the first activities at the crime scene are essential for the successful preservation of the physical evidence. The first responder and ultimately the crime scene investigator have the obligation to make the scene secure and ensure that any further activities at the scene do not change the evidence. The use of a multilevel security method would accomplish this task. The preliminary scene survey is the first on-scene activity. Precautions are taken for transient and conditional evidence during the survey.
All forensic photography must consider three elements at a crime scene: the subject, the scale, and a reference object. Also, the overall forensic photographs must be shown a neutral and accurate representation.

Features of crime scene photography.

Common photography related to creative and artistic photography often shows their results in a different way. Creative and artistic photographs are perfectly fine. However, the forensic photography is different. They should serve several purposes.
For people who were at the original crime scene, forensic photos will help refresh their memory as time goes by. People who could not be present at the original crime scene, it provides them with the opportunity to see the crime scene and the evidence within the crime scene.
Furthermore, the forensic photos can be utilized by law enforcement professionals who will become involved with crime and will be utilized later when the crime case goes to trial. Judge, jury, attorney and witnesses can reuse and utilize forensic photos for lawful evidence or references. Sometimes, forensic photos can be the only way to collect lawful evidences; therefore, two key points are important:
  1. Documentation of the crime scene and the evidence within the crime scene.
  2. Collection of evidence. These images can then be later used as examination-quality photographs by experts/analysts from the forensic laboratory.

    Crime scene evidence

Crime scenes are the source of the physical evidence that is used to associate or link suspects to scenes, victims to scenes, and suspects to victims. Any item found at a crime scene can be physical evidence; it can be labeled as the debris of criminal activity. There is considerable overlap among identifications, but evidence can be categorized into the following broad groups based on its origin, composition, or method of creation:
  1. Biological evidence — any evidence derived from a living item. Includes physiological fluids, plants, and some biological pathogens.
  2. Chemical evidence — any evidence with identifiable chemicals present.
  3. Patterned evidence — any evidence with a pattern or predictable pattern of appearance.
  4. Trace evidence — any evidence of such a small size so as to be overlooked, not easily seen or not easily recognized.
In addition to identifying the type of physical evidence found at a crime scene, it is necessary to obtain valuable investigative information from the analysis of the items of physical evidence.
  1. Determination of corpus delicti — the evidence is used to determine if a crime has taken place.
  2. Modus operandi identification — criminals repeat behavior. Repeated methods of entry, for example, by kicking in a back door with the same shoe leaving the same footwear impressions throughout the crime scene.
  3. Association or linkage — the Locard Exchange Principle — transfer of evidence by contact. See the next section to follow.
  4. Disproving/supporting victim/suspect/witness statements — the evidence may or may not support what these groups say.
  5. Identification of suspects/victims/crime scene location — fingerprints and even DNA can be used to identify who was present at a crime scene.
  6. Provide for investigative leads for detectives — the use of the physical evidence to give information to detectives that will assist them in locating victims and suspects.

    Essential 3 steps on crime scene

The first activities at the crime scene are essential for the successful preservation of the physical evidence.

First responders

The crime scene investigator is rarely the first person at a crime scene. Most first responders work on reflex or instinct at the scene. Their tasks are to save lives or apprehend suspects. Unfortunately, that may mean that physical evidence may be inadvertently altered, changed, or lost due to the actions of a first responder. The crime scene investigator needs to communicate with the first responders to determine if any changes or alterations have occurred at the scene before the scene investigator arrived.

Crime scene security

Locard's exchange principle is the basis for the use of physical evidence in a criminal investigation, it is extremely important for the crime scene to be made secure and restrict the access to the crime scene by nonessential people. Many agencies allow easy access to crime scenes by anyone in the agency. Most media persons are kept out but changes to the scene and evidence can change in attempts to protect victims.

Preliminary scene survey

The preliminary scene survey or walk-through is the crime scene investigator’s first opportunity to view the target area crime scene. A simple visual search for obvious physical evidence can be accomplished at this time. It is during this first viewing of the crime scene that the scene investigator should note any transient or temporary items of evidence and protect them immediately. Melting snow footwear impression are examples of this transient evidence.

Methods

All photographs must contain three elements: the subject, a scale, and a reference object. Crime scene photographs should always be in focus, with the subject of the photograph as the main object of the scene. There should always be a scale or ruler present. This will allow the investigators the ability to resize the image to accurately reconstruct the scene. The overall photographs must be a fair and accurate representation of what is seen. Any change in color may misidentify an object for investigators and possibly jurors.
Preliminary overall photographs should attempt to capture the locations of evidence and identifying features of the scene, such as addresses, vehicle identification numbers and serial numbers, footwear/tire mark impressions, and the conditions of the scene. While the purpose of the overall photograph is to document the conditions of the scene and the relationship of objects, the medium range photograph serves to document the appearance of an object.
In all photographs, a scale must be included, as well as a marker to indicate the identity of the object in question. Again, objects of medium-range photographs must be a fair and accurate representation of what is seen. Adjusting the photographic principles or lighting may allow the photographer to achieve this goal.
Above picture is Figure 3.1. Which one is the correct representation?
In Figure 3.1, Photograph 2 is a correct representation.
Photograph 1 has too much light. It means that the photographer failed to catch proper light to describe object. By adjusting the flash, photographer should adjust camera flash to capture the object.
In general, the basic components of macro or evidentiary photography are as follows:
If any evidentiary photographs are to be taken for use in a critical comparison examination at a later time, guidelines must be followed in accordance with the best practices of digital evidence.
  1. The digital image must be captured in a lossless compression format. The two widely accepted lossless compression formats are tagged image file format and RAW. TIFF is a universal file type, whereas RAW files are proprietary based upon the manufacturer of the camera. Specialized software may be required to open and enhance a RAW image.
  2. The camera must be on a grounded platform, such as a copy stand or tripod. In general, the human body cannot stop natural vibrations with a camera shutter speed slower than 1/60 of a second. Using a grounded platform will allow the subject matter to be in complete focus.
  3. The camera shutter must be controlled by a remote cord or by using the timer mode.''' The simple action of depressing the shutter control will cause the camera to vibrate, losing focus of the subject matter.

    Documentation

The responding officer must also maintain a photo log if any photographic documentation is taken. The log should contain the date and time of the photograph, the subject matter, and any additional notes. These logs must be maintained within a case file or incident report, as they are a part of the examination record and discoverable material at trial.

Digital photography

Photographers must understand principles of photography first. When the photographers take the photographs itself, they must consider three components. The three components are ISO, Shutter speed and aperture.
The International Organization for Standardization is an international standard-setting body composed of representatives from various national standards organizations. The actual meaning in photography is a camera’s sensitivity to light
ISO
By adjusting ISO, the photographs can be shown differently in same environment. In dark environment, ISO makes light sensor of camera more sensitive. It helps photographers to meet proper light in dark or harsh condition. Among above two photographs, the photograph 2 is a proper representation because it shows clear objects with proper brightness. However, ISO has high possibility to make camera noise which is visual distortion. Too much dependence on ISO can distort the image. For that reason, the photographers must understand ISO before using it.
Shutter speed
Shutter speed is the length of time when the film or digital sensor inside the camera is exposed to light. Object and image can be shown differently by shutter speed. Below are the examples.
These two photographs are taken under same situation except for camera shutter speed.
In above situation, slow shutter speed makes image more clear and bright because the low shutter speed takes more light than high shutter speed. However, the high shutter speed often is necessary for moving object.
Above two photographs are taken under same situation except for camera shutter speed.
In case of moving object, the low shutter speed is not proper to capture the object. It needs faster shutter speed to capture it. Shutter speed has pros and cons.
For capturing a moving object, photographers must use a high shutter speed. However, the image can be very dark. Low shutter speed must be used when capturing a clear image or object under the harsh condition, but it is hard to capture the moving objects.
Aperture
Aperture means that the extent of a sharpness of an image that is shown through the lens. So, it is one of really important things to photographers. High aperture means hard sharpness like photograph1. Every Low aperture means soft sharpness.
The photograph 1 shows all objects very clearly because of the high aperture. The photograph 2 image shows an object with right focus but rest of the objects are all blurred because of low aperture.

Use of flash

External flash units are helpful tools when responding to a crime scene and for the proper documentation of evidence. The white balance of a photo flash unit is set to mimic daylight to ensure the proper color balance of the subject matter. The photographer must be mindful of the reflections that can occur due to the directionality of the flash and the position of the subject matter. To avoid flash reflections, as demonstrated below examples, the flash must either be removed from the camera body, creating an angle, or bounced off of the ceiling.

Equipment

The tools required to properly document the crime scene include:
The images must be clear and usually have scales. They serve to not only remind investigators of the scene, but also to provide a tangible image for the court to better enable them to understand what happened. The use of several views taken from different angles helps to minimise the problem of parallax. Overall images do not have scales and serve to show the general layout, such as the house where the murder is thought to have occurred. Context images show evidence in context, like how the knife was next to the sofa. Close up images show fine detail of an artifact, such as a bloody fingerprint on the knife.
Road traffic incident photographs show the overall layout at the scene taken from many different angles, with close-ups of significant damage, or trace evidence such as tire marks at a traffic collision. As with crime scene photography, it is essential that the site is pristine and untouched as far as is possible. Some essential intervention, such as rescuing a trapped victim, must be recorded in the notes made at the time by the photographer, so that the authenticity of the photographs can be verified.
As with all evidence a chain of custody must be maintained for crime scene photographs. Sometimes a CSI will process his/her own film or there is a specific lab for it. Regardless of how it is done any person who handles the evidence must be recorded. Secure Digital Forensic Imaging methods may be applied to help ensure against tampering and improper disclosure. Accident scene pictures should also be identified and sourced, police photographs taken at the scene often being used in civil cases.

Analysis of historic photographs

Crime or accident scene photographs can often be re-analysed in cold cases or when the images need to be enlarged to show critical details. Photographs made by film exposure usually contain much information which may be crucial long after the photograph was taken. They can readily be digitised by scanning, and then enlarged to show the detail needed for new analysis. For example, controversy has raged for a number of years over the cause of the Tay Bridge disaster of 1879 when a half-mile section of the new bridge collapsed in a storm, taking an express train down into the estuary of the river Tay. At least 75 passengers and crew were killed in the disaster.
The set of photographs taken a few days after the accident have been re-analysed in 1999–2000 by digitising them and enlarging the files to show critical details. The originals were of very high resolution since a large plate camera was used with a small aperture, plus a small grain film. The re-analysed pictures shed new light on why the bridge fell, suggesting that design flaws and defects in the cast iron columns which supported the centre section led directly to the catastrophic failure. Alternative explanations that the bridge was blown down by the wind during the storm that night, or that the train derailed and hit the girders are unlikely. The re-analysis supports the original court of inquiry conclusions, which stated that the bridge was "badly designed, badly built and badly maintained".

Concerns over scientific validity

A 2019 ProPublica investigation found that despite frequent use by the FBI, there are considerable concerns over scientific validity of the FBI's analysis of photographic evidence. ProPublica "asked leading statisticians and forensic science experts to review methods image examiners have detailed in court transcripts, published articles and presentations. The experts identified numerous instances of examiners overstating the techniques’ scientific precision and said some of their assertions defy logic."