How Infrared Photography Helps in Crime Scene
Today we will talk about a very interesting topic: How Infrared Photography Helps in Crime Scene. In addition to the record and situation plan, photography is one of the standard and mandatory procedures for establishing the factual situation at the scene of the crime and securing the traceological chain of evidence.
Numerous authors dealing with forensic photography describe the very wide possibilities of using photography in the infrared range, starting with the detection and documentation of fingerprints, biological traces, gunshot wounds, tattoos, examination of disputed documents; up to the documentation of autopsy findings and other identification features.
We would also like to share with you our other articles on infrared photography such as How Infrared Photography Works in General or Camera Settings for Infrared Photography.
- How Infrared Photography Helps in Crime Scene: Basic Principles
- Equipment for Recording Infrared Photos in Criminalistics
- Conclusion
- FAQ
- How Infrared Photography Helps in Crime Scene?
- What types of equipment are needed for infrared photography?
- How is infrared photography different from other types of photography?
- What are some limitations of infrared photography in crime scene investigations?
- How is infrared photography used in conjunction with other forensic techniques?
- What are some examples of cases where infrared photography was used to help solve a crime?
How Infrared Photography Helps in Crime Scene: Basic Principles
Infrared photography is a technique used in artistic photography, but also in forensic science, where it enables the detection and documentation of objects that are invisible to the human eye under normal conditions. To understand how infrared photography helps in crime scene, we need to know that the light visible to humans is in the spectrum of electromagnetic radiation with a wavelength of about 380 nm to 750 nm (Figure 1).
Below the lower limit (10 nm – 380 nm) is the area of ultraviolet (UV) radiation, while the area above the upper limit of the visible spectrum (750 nm – 1 mm) is called the area of infrared (IC) radiation. In the context of infrared photography, a particularly important part of infrared radiation, is the so-called near-infrared region (near infrared – NIR) in the wavelength range from about 750 nm to 1400 nm, because it is in the area that can be recorded by the sensors of digital cameras.
The basic property that makes infrared photography applicable in forensic science is that it sometimes makes it possible to distinguish objects that look almost the same in the visible light range based on their different behavior when exposed to infrared light.
Namely, when the object is photographed in such conditions – then there are three possible outcomes:
1) The object will absorb infrared radiation and become darker
2) The object will reflect infrared radiation and become brighter or completely white
3) The object will transmit infrared radiation, become invisible and thus reveal what is under it. A photo created by such a process, by reflecting infrared light from the object being photographed, is called reflective infrared photography.
In addition to what has been said, there is also the possibility that the object will convert infrared radiation into radiation of a longer wavelength, that is, cause luminescence in the infrared spectrum. Luminescence is usually induced by an excitation light source with a wavelength of about 450 nm or about 514 nm, and such photography is called luminescent infrared photography. The luminescent properties of substances are relatively rare and are mainly used for testing different inks during the forensic analysis of disputed documents.
Equipment for Recording Infrared Photos in Criminalistics
As a rule, all cameras can record a part of the infrared spectrum with their sensors, but manufacturers of better quality cameras install filters on the sensors to block infrared light, the so-called hot mirror filters, due to which light of the visible spectrum mainly reaches the sensor.
This improves the optical properties of the camera, reduces chromatic aberration, and brings the general appearance of the image closer to what can be seen with the naked eye, especially in terms of the reality of color reproduction.
For this very reason, it is difficult for classic digital SLR cameras to take infrared photos without modifying the camera and/or using additional equipment. Today, there are several available solutions, all of which have certain advantages and disadvantages, starting from price, image quality, and to practicality and speed of use, which is why there are no unique and standardized ways of selecting equipment intended for use in a forensic context.
The most accessible and cheapest solution is certainly the use of simple compact cameras or cell phone cameras, which do not have filters to block the infrared spectrum of light or for which these filters are less effective. Whether one of these cameras is suitable for taking infrared photos cannot be known in advance, but there is a simple way to check it.
Namely, it is enough to point the TV remote control towards the camera and press any of the buttons. If the light from the front of the steering wheel can be seen on the image or the camera screen, it means that the camera can record infrared light and, in combination with some of the filters that block light from the visible area, can be used to take infrared photos.
How advisable this solution is to be used in forensics is really doubtful, taking into account that due to the quality of the photos and the weaker possibilities of controlling the camera in forensics, the use of compact cameras is by no means recommended.
Another possibility is the use of special cameras whose basic purpose is to take infrared photos and use them for scientific purposes (in the police, army, medicine and research activities). Unfortunately, the market for such specialized cameras is scarce.
As far as is known, there is currently only one such camera model commercially available (Fujifilm X-T1 UV/IR), while it is much easier to obtain modified models of standard DSLR cameras or adapt an existing DSLR camera for the needs of infrared photography.
Converted DSLR cameras are most often used for taking infrared photos. Ready-made customized cameras can be purchased on the market or you can use the services of companies that deal with the customization of photographic equipment, and it is also possible to modify the camera yourself according to the instructions available on numerous websites.
Conclusion
The role of photography in forensics is not only documenting the scene, but also discovering and documenting invisible and poorly visible traces, and it can also be a means of evidence when it is not possible to physically remove the traces from the scene. In this context, infrared photography is especially important, as it enables the visualization of traces based on their different properties of absorption, reflection and transmission of infrared radiation.
Infrared photography is suitable for detecting and/or improving the visibility of various types of tracks. Its application is successful on traces of blood on dark and multi-colored surfaces, as well as on surfaces that have been discolored or affected by the fire.
It can also be used to detect traces of gunpowder particles on dark materials and to improve the visibility of traces of papillary lines on multi-colored backgrounds. Research also shows its applicability in detecting and documenting poorly visible, altered and laser-removed tattoos, bruises and bite marks, and sometimes in documenting autopsy findings.
Taking infrared photos does not require large investments, but it is enough to remove the filter that blocks infrared radiation from the DSLR camera and use one of the filters that block light from the visible spectrum. Although the shooting method does not differ much from standard photography, many material properties affect the results, so the outcome is often uncertain and there are no universally applicable settings.
FAQ
How Infrared Photography Helps in Crime Scene?
What types of equipment are needed for infrared photography?
How is infrared photography different from other types of photography?
What are some limitations of infrared photography in crime scene investigations?
How is infrared photography used in conjunction with other forensic techniques?
What are some examples of cases where infrared photography was used to help solve a crime?
Infrared photography has been used to help solve many different types of crimes, including homicides, robberies, and burglaries. For example, in one case, infrared photography was used to locate the body of a murder victim who had been buried in a shallow grave. In another case, infrared photography was used to reveal hidden footprints that led to the arrest of a burglary suspect.
