Introduction to the Matching Method The method we have developed for comparing two tracks is summarized as follows: 1. Digitize the Tracks - The tracks are scanned with a desktop document scanner. High resolution digital photographs will also suffice provided they are taken under standardized conditions (zoom and distance from the track). 2. View the Images - Tracks are compared only with other tracks that seem to have been made by the same foot, i.e., left front tracks are compared only with other left fronts. The two images to be compared are opened simultaneously using standard image processing software. (We like ImageJ, a powerful program available at no cost over the Internet.) The images are superimposed, one atop the other so that only one may be viewed at a time. 3. Compare - Switch rapidly back and forth between the two images (easily accomplished with ImageJ by repeatedly pressing the Tab key). If the tracks were made by the same individual and are appropriately aligned with respect to each other on the computer screen, then the portions that are similar will be apparent. What Does a Match Look Like? To see this effect look at the animated images below. Each animation continuously switches between two small portions of a left front track. The images on the left were made by two different feet and do not match well. Those on the right, however, were made by the same foot and have been properly aligned. The effect of apparent motion is the indication that they match very well. When the extent of the area in motion includes a sufficient number of dots you can be reasonably certain the two tracks were made by the same individual. 
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