Two images are compared to determine how similar they are. First, a process normalizes each image, then horizontal and vertical byte sequences are derived from each image. A similarity formula is used to obtain a similarity value that represents the similarity between the two images. An approximate pattern matching algorithm is used to determine the error distance between the horizontal byte sequences for the images and to determine the error distance between the vertical byte sequences for the images. The error distances and the length of the byte sequences are used to determine the similarity value. Padding is used to make the aspect ratios the same.