There is provided an image similarity calculation system which yields a large value for image similarity between an edited image and an original image. A local region weight calculation means 14 calculates a weight value for each local region in the image as a local region weight value, based on probability of editing each local region in the image. The local region weight calculation means 14 outputs the calculated local region weight value to an image similarity calculation means 122. A small region similarity calculation means 121 compares a feature quantity for each small region resulting from dividing an inquiry image with a feature quantity for each small region resulting from dividing a reference image. The small region similarity calculation means 121 calculates a similarity of feature quantities for the respective small regions. The image similarity calculation means 122 calculates an image similarity between the inquiry image and the reference image by applying a small-region-based weight value to the calculated similarity. This weight value is found from a local region weight value supplied from the local region weight calculation means 14.