Image Processing Reference
Figure1.26 Magazine cover (top) and details imaged with visible light (bottom left) and
shortwave-UV light (bottom right). (Courtesy of Sirchie Fingerprint Laboratory)
detector. There are many other forensic materials (urine, semen, hair, fibers) that
do fluoresce in the presence of ultraviolet light. In that case, the investigator's eyes
can detect the visible fluorescence, and he or she need only employ an ultraviolet
light source such as a black light.
Reflected ultraviolet light photography can sometimes be used to detect bruises
and wounds such as bite marks many weeks after the wounds were inflicted,
when the wounds are virtually undetectable to the naked eye. The wounds exhibit
a change in pigmentation that may be caused by disturbance to the pigment
production of the injured basal cells. 10 Figure 1.27 shows examples of an old bite
mark that is still visible to reflected-UV imaging.
Many organic materials such as waxes, oils, adhesives and paints absorb or
scatter UV light strongly. Figure 1.28 shows a terra cotta tile floor with a shoe
impression that is only apparent to near-UV imaging.
The impression was formed by an epoxy floor sealant that was tracked onto the
tile floor by a workman. The epoxy tends to scatter UV light, making it look white
in the image.
Figure 1.29 shows a vinyl floor tile which has been covered with floor wax. A
shoe impression shows up quite dramatically in the near-UV image relative to the
10 R. Barsley, M. West, and J. Fair, “Forensic Photography — Ultraviolet Imaging of Wounds on Skin,”
TheAmericanJournalofForensicMedicineandPathology11(4), 300-308 (1990).