UV and IR Photography in Forensic
The use of photography is documenting a crime scene or recording an autopsy procedure is increasingly becoming an integral part of forensic investigation processes. Besides witness statements, the physical evidence collected from crime scenes and reposts made by crimes scene investigation, infrared and ultraviolet photography techniques are used to provide a detailed and accurate account that is unalterable. In many criminal cases, photographic evidence is critical for both defense and prosecution counsel. Additionally, photographic evidence is often used to display or reconstruct the nature of crime scenes to crime scene investigators who could not make it to the actual scene. This paper explores the application of infrared (IR) and Ultraviolet (UV) photography in forensics.
The documentation of physical evidence through forensic photography is one of the integral aspects of crime scene investigations. Ensuing analysis of photographs taken from crime crimes, gunshot wounds, bite marks, trace evidence and autopsy procedures among others often produces clues investigators can use effectively to reconstruct some of the events of an incident under investigations, or yield enough evidence to gain a conviction at trial. Conventional photography documents images in the visible light spectrum, and often records images on digital file or film visible to the human eye. In that regard, traditional photography limits the use of photography in documenting the evidence essential to reconstruct facts of a given case. For several years, forensic photographers have come up with various specialized techniques for documenting critical evidence, especially under challenging situations. Infrared (IR) and Ultraviolet (UV) photography can be applied in various scenarios to produce results that are often limited by traditional photographing techniques in the visible light spectrum. The interest behind the exploration of the application of UV and IR photography in forensics pertains to their capability to document injuries due to biochemical and biological changes that arise after injuries. The subsequent subsections explores the application of UV and IR photography in forensics
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UV Photography Application
Photographic accuracy in cases involving bite marks is vital to an investigative process because the bite mark may be the only evidence linking a suspect to the crimes under investigation. For this reason, the push to use superior photographic technique is unavoidable in the investigative process. Ultraviolet radiation has been used to improve the visibility of old wounds, bruising and bite marks has been documented in various studies. Documenting bite marks and bruises through UV photography requires specialized UV components. However, acquiring the necessary ultraviolet forensic photography equipment can be taxing. This implies that the digital camera used for this purpose must either be designed or modified with ultraviolet acquisition in mind. Another important point to highlight regarding UV photography is that better results are influenced by the power of the light source. In other words, there is a need for a more powerful light source for illumination during ultraviolet imaging. In contrast to alternate light imaging (ALI) and IR, ultraviolet images depict the surface disruption of the human skin when the UV imaging technique is used to document bite marks.
Adequate examination of injuries of victims of violence, both deceased and living, is vital for the reconstruction of suspected criminal incident. The use of medical reports by the prosecution counsel on injuries are evidence demands a detailed description and accurate interpretation of the reported injuries. The prosecution counsel faces difficulties, especially when there is lack of visibility of the reported injuries. Difficulties may be due to, for instance, a bruise in a yellow appearance or due to healing of the injury. Additionally, even the most recently caused bruise might also be invisible at the surface of the skin. As an area of interest, improving the visibility of injuries that are often not visible to the naked eye is vital in gaining a detailed and accurate documentation of injuries reported by a victim of violence. To recap, prints or documented images of UV photography appear as regular black and while photos. However, after the development of reflected UV photography film, they can be made into enlargements or slides. The use of UV photography in forensics can greatly improve an investigation by illustrating an outline of a weapon that caused an injury and show history of injuries.
IR Photography Application
The use of infrared-aided photography has been documented, especially in the detection of gunshot residues in fabrics. Accurate photographic recording of a crime scene is an important pillar of any effort into the collections of evidence, especially when it applies to documenting gunshots injuries or fatalities inflicted during crimes of violence. For IR photography, a source of the infrared radiation is mandatory. Many alternative light source systems are equipped with IR components. However, most of the contemporary flash units emit visible, IR and UV light. This makes it possible to apply IR techniques in bother laboratory and field environments. Additionally, advances in photographing technologies has resulted in digital imaging options for forensic photographers in both environments. Infrared photography techniques can be used to examine document forgeries and alternations. Differentiating between visibility identical pigments and inks is characterized by observing any slight difference in the way they absorb or transmit IR radiation. Infrared luminescence and reflected photography is also used to reveal printing and writing under obliterations on important physical documents. Furthermore, illegible worn, aged or charred documents can be rendered legible in IR photographs.
The physical properties of fabrics and the dyes used in the same cloth affects the manner in which IR radiation is absorbed or reflected. Reflected IR can be useful in forensic investigations where there is a need to differentiate between clothing fabrics that are visibly similar in visible light, yet they are actually different. One of the intriguing application of reflected IR photography pertains to the reduction of background on fabric that are either dark or with busy pattern to display the presence of stains. In that regard, substances such as gunshot residues or blood patterns can be revealed in scenarios where conventional photographic techniques are limited. Gunshot residue is also revealed using IR reflected photography. In addition, a fabric with visibly dark or busy pattern is often rendered as a less distracting pattern or a single pattern; hence, revealing any important detail hidden from the unaided eye. Another intriguing application of IR photography relates to the documentation of injuries and biomedical uses. IR energy can penetrate the human skin 3 millimeters deep. In addition, IR energy is absorbed by blood. According to Broux, McCaul and Shimamoto, these aspects are exploited to show details 3 millimeters below the human skin. Reflected IR and reflected UV photographs can be used to show the details below a victims skin surface and details on the surface of the skin respectively. To that end, bite marks can be documented using reflected IR photography. To conclude, forensic applications of reflected infrared photography include biomedical photography, gunshot residue visualization and bloodstain documentation.
Routine application of infrared and ultraviolet photographing techniques in the not only forensic, but also biomedical fields is not new. Forensic photography is essential in documenting crime scenes, autopsy procedures, bite marks, gunshot wounds, weapons and trace evidence. In line with their efficiency in yielding clues for investigators to use in the reconstruction of facts regarding a particular case, UV and IR photography plays a significant role in helping courts establish the whys and how behind cases. Biting and gunshot injuries might be complex; thus, the collection, analysis and interpretation of evidence must the handled with care irrespective of the forensic photographing technique used. Acquiring reproducible and accurate forensic images is that one of the components of an effective crime scene investigation, but an important one. Therefore, a forensic photographer should be able to employ the most effective protocol to yield the best results.