Forensic dental photography 233
light spectrum from the ultraviolet band, with ultraviolet light being about
one-half of the wavelength of infrared light. Because infrared is longer in
wavelength transmission, it penetrates up to 3 mm below the surface of the
skin (Figure 11.39).
Since the depth of the injury that will be recorded with the infrared tech-
nique is below the surface, the infrared focus point will not be the same as the
visible focus point, requiring a focus shift. The field of digital infrared forensic
photography has grown to include documentation of gunshot residue, tattoo
enhancement, questioned documents, blood detection, background deletion,
wound tracking, and tumor detection. The injury documented with infrared
technique will not appear the same as photographs taken using visible light.
In Kodak Publication N-1, Medical Infrared Photography,^6 this difference is
discussed (pp. 26–27): “It should not be overlooked that even when the lens is
focused correctly, the infrared image is not as sharp as the panchromatic one.
The reason is the lens aberrations have been corrected for panchromatic pho-
tography, so the anastigmatism is not as perfect in the infrared. The majority
of biological infrared images are formed from details not on the outside of
the subject.... This feature accounts for the misty appearance of many infra-
red reflection records.”^32
Successful infrared photography is a trial-and-error process, particu-
larly when dealing with injury patterns. If the injury did not cause sufficient
damage to the deeper skin tissues, i.e., no bleeding below the surface of the
injured skin, or if the surface of the injured skin is too thick for the infrared
light to penetrate to find the site of the bleeding, there may be no infrared
detail recorded in the photographs. The advantage of digital photography
is that the image can be either previewed before or immediately seen after
Figure 11.39 ir image of the same dog bite as seen in Figures 11.32 and 11.33.
Note the deeper level of penetration of IR energy into the tissue.