1. An image retrieval system comprising: an image entry unit configured to receive as input an image, the image entry unit being configured to transform the image into a binary image; a descriptor determining unit comprising: a first transforming unit configured to transform the binary image into an intermediate image, wherein the intermediate image is a grayscale image, and a second transforming unit configured to generate a descriptor of the image from the intermediate image; an image comparing unit configured to compare the image with one or more candidate images by comparing the descriptor of the image with descriptors of the one or more candidate images; and a retrieving unit configured to retrieve at least one of the one or more candidate images similar to the image based on the comparison of their descriptors.