Three Levels of Detail - Advanced 
Footprints from the left feet usually are found on the left side of the track plate's contact paper, although this is not always the case. Toes 2-5 of the fore feet generally angle toward the medial side. Although rarely present, the impression made by the first toe introduces an unambiguous asymmetry that distinguishes left from right. The outline of the metacarpal pad typically displays asymmetry for front feet. Toes 2-5 of the rear feet tend to point straight ahead and the impression made by the metatarsal pad is usually much more symmetric than the corresponding portion of a front print. Sometimes examination of these gross details does not result in a clear indication. In such cases observation of the second-level details will often be convincing. Typical row patterns are more or less bilaterally symmetric, with left and right metacarpal pads being, at least roughly, mirror images of each other. This is most evident in the location of the center of curvature for the arcs formed by each row of dots. In the right-foot print, this center is located in the upper right of the main portion of the metacarpal pad. In the left foot’s print, this center is located in the upper left portion of the pad. Range of Variation in Feet Although there is some variation in the row patterns (the second level of detail) between individuals this has not proven to be particularly useful for distinguishing between individuals. Consider these three right metacarpal prints generated from museum specimens. All are rather similar in their overall pattern. Keep in mind that tracks gathered from wild fishers are never this clear and complete. 
Prints of the right metacarpal pad of three different
fishers -
Range of Variation in Prints of a Single Foot Identifying individual fishers from their footprints depends on a certain degree of consistency in the patterns across multiple prints made by the same foot. The two images below show portions of two different prints made by the same foot. Twelve pairs of dots are highlighted in the first image, each pair corresponding to a pair of wart-like bumps on the botton of the fisher's foot. The second image shows the dots made by these same 12 pairs of warts. Careful measurements of the dot pairs in these and other prints made by this foot reveal that, although the size of the dots may change somewhat (as seen here - the dots in the second image tend to be larger than those of the first) the centroid-to-centroid spacing is quite consistent, making it possible to compare this spacing between footprints as a way of telling if they were made by the same foot. 
Portions of two prints made by the same foot, with corresponding dot pairs highlighted in each. Back to Basics
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