Two faces may be compared by calculating distances between different regions of the windows, and choosing one of the distances as the difference between the images. Two images are examined to detect the location of the face in the images. The faces may then be geometrically and photometrically rectified. A sliding window that is smaller than the whole face may be positioned at various locations over the images, and a descriptor is calculated for each window position. The descriptor for a window at one location in one image is compared with descriptors for windows in the neighborhood of that location in the other image. The lowest distance between window descriptors is chosen. The process is repeated for all window positions, resulting in a set of distances. The distances are sorted, and one of the distances is chosen to represent the difference between the two faces.