Abstract: A system for comparing a subject image against a reference image for determining the closeness of match, or against a plurality of reference images for determining the one of the reference images which corresponds to the closest match. The closest match is determined in response to the extrema of light transmitted through complementary versions of the images. More specifically, the present system compares the true subject image against the complement of each reference image, and the complement of the subject image against each true reference image. Alternatively, the true subject image is compared against each true reference image, and the complement of the subject image against each complement reference image. The particular reference image which achieves a preselected minimum or maximum of transmitted light for each such comparison is selected as the image which most closely matches the subject image.