Forensic photography uses specialised techniques to document investigations, often revealing details imperceptible to the naked eye. Besides recording the original appearance of a crime scene, photographs often help trigger memories of witnesses and investigators when trying to recall details of an event. Further, they can be used as evidence to support verbal testimony.
Infrared photography records images through infrared radiation as opposed to light. This method is especially useful in surveillance photography and aerial shots at night. Infrared also may be employed to detect gunshot-powder burns and bloodstains in clothing, as well as certain types of secret writing (i.e., invisible ink). Almost any 35mm film camera or lens can be used for this type of photography. The infrared image is captured by special film that is heat-sensitive.
Investigators use ultraviolet (UV) photography when visible light and infrared photographic methods fail. After being dusted with fluorescent powder or Ninhydrin, UV photography may capture unseen fingerprints on multicoloured surfaces. It also can reveal bodily secretions such as urine, semen and perspiration not visible to the naked eye. Though standard film (at a higher than average speed) may be employed for ultraviolet photography, a special filter that excludes all visible light will need to be used.
Multiple Exposure Photography
Different sources of lighting may reveal different details in a piece of evidence. For instance, a single exposure may not capture an entire fingerprint on a murder weapon. Different amounts of UV light may be required to reveal the latent in its entirety. In forensic photography, one solution involves exposing the same shot multiple times so that details in various light ranges can be superimposed one atop another. In the digital age, however, layering individual shots in Photoshop and merging them usually allows a great deal more control than trying to attempt the process in a camera.
Digital cameras have made forensic photography a great deal faster and easier. Instead of rushing back to a darkroom to develop a roll of film, the photographer has an instant image that can be shared with investigators. Generally, digital photographic evidence is admissible in court, though sceptics have argued that its reduced resolution and ease of alteration make it inferior to traditional film-based methods. However, stringent documentation policies and procedures, as well as continuing technical advances usually should dispel any doubts as to the validity of digital evidence.
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- Forensic Science Central: Photography
- Crime Scene Investigator Network; The Admissibility of Digital Photographs in Court; Steven B. Staggs; May 2001
- Crime Scene Investigator Network; Multiple Exposure Method in Digital Photography of Fingerprints, From the Journal of Forensic Identification, Vol. 55, No. 5, September/October 2005; Alan Chaikovsky, et al.; May 2008
- Crime Scene Investigator: Infrared Photography
- Crime Scene Investigator: Ultraviolet Photography