1. An image processing apparatus, comprising: a first local feature value generation unit that detects one or more of first feature points from a first image, and calculates, from a region of a preset range encompassing each first feature point detected, a set of information about first local feature values corresponding to each first feature point; a correspondence point calculation unit that calculates, as information about correspondence point(s), a correspondence relation between the first feature point(s) and a second feature point(s) contained in a set of information about second local feature values calculated from a second image; a relative correspondence point scale size calculation unit that calculates, as information about relative scale sizes of correspondence points, a relationship between a scale(s) of the first feature point(s) and a scale(s) of the second feature point(s), based on the set of the information about the first local feature values, the set of the information about the second local feature values and the information about correspondence points; a correspondence point selecting unit that, based on the information about the relative scale sizes of the correspondence points, performs clustering on at least one out of the first feature point(s) and the second feature point, and selects at least one feature point based on an outcome of the clustering; and a decision unit that, based on the feature point(s) selected by the correspondence point selecting unit, compares the first image and the second image with each other, from cluster to cluster, and decides on possible photographic subject identity.