Method and apparatus for alignment, comparison and identification of characteristic tool marks, including ballistic signatures

Abstract

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. Computer numerically controlled positioning of the toolmark relative to imaging sensors which use fixed focus optics with shallow depth of focus, varying focus distance and orientation systematically to construct a sequence of images, maximizes reliability of resulting images and their comparisons.