Aligning Shoeprint Images that have nonlinear distortion effects

Shoeprints are aligned before assessing similarity, and automatic alignment algorithms can handle differences in translation, rotation [1], and scale. But shoeprints recorded at a crime scene may be partials photographed at an angle without an L-scale, with perspective or other non-linear distortions. How is shoeprint alignment affected by nonlinear distortions in the questioned impression? To find out, we took a few images f rom the ShoeCase [2] database, distorted them by 5, 10, and 20 degrees with the warp tool in Photoshop, and then aligned them to mated and close-nonmated reference prints.