A method for image comparison includes reading from a memory in a computerized image processor a source image and a target image. The source and target images are segmented, using the image processor, into respective pluralities of source and target arrays, respectively including source and target array elements, each array element including a matrix of one or more pixels from a respective image, each of the source arrays having a respective position in the source image, and each of the target arrays corresponding respectively to one of the source arrays based on the respective position. An asymmetric warping process is applied between each of the source arrays and each of the respectively corresponding target arrays so as to compute respective array similarity scores. The respective array similarity scores are combined so as to compute an image similarity score of the target image with respect to the source image.