1. A differing region detection system, comprising: a difference information generating unit configured to generate inter-image difference information indicating a difference in feature amounts for each subregion between first and second images based on a first feature amount vector that is a set of feature amounts respectively corresponding to a plurality of subregions in the first image and a second feature amount vector that is a set of feature amounts respectively corresponding to a plurality of subregions in the second image; and a differing region detecting unit configured to detect a differing region that is an image region that differs between the first and second images, based on differences in the respective subregions indicated by the inter-image difference information, and output detection information indicating a result of the detection.