Systematic use of infrared imaging characterizes marks made on items and
identifies the particular marking tool with better accuracy than use of
visual imaging. Infrared imaging performed in total darkness eliminates
shadows, glint, and other lighting variations and artifacts associated
with visible imaging. Although normally used to obtain temperature
measurements, details in IR imagery result from emissivity variations as
well as thermal variations. Disturbing an item's surface texture creates
an emissivity difference producing local changes in the infrared image.
Identification is most accurate when IR images of unknown marks are
compared to IR images of marks made by known tools. However, infrared
analysis offers improvements even when only visual reference images are
available. Comparing simultaneous infrared and visual images of an
unknown item, such as bullet or shell casing, can detect
illumination-induced artifacts in the visual image prior to searching the
visual database, thereby reducing potential erroneous matches.