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; outputs a set of first scale information, the set being made up of scale sizes of each of the first feature points; generates first local feature values of a region of a preset range encompassing each of the first feature points; and outputs a set of information about first local feature values, the set being made up of the first local feature values; a second local feature value generation unit that detects one or more of second feature points from a second image; outputs a set of second scale information, the set being made up of scale sizes of each of the second feature points; generates second local feature values of a region of a preset range encompassing each of the second feature points; and outputs a set of information about second local feature values, the set being made up of the second local feature values; a correspondence point calculation unit that calculates, as information about correspondence point(s), a correspondence relation between the first feature point(s) and the second feature point(s) based on the set of information about first local feature values and the set of information about second local feature values; and outputs a set of information about correspondence points, the set being made up of the information about correspondence point(s); 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 first scale information, the set of second scale information and the set of information about correspondence points; and outputs a set of information about relative scale sizes of correspondence points, the set being made up of the information about relative scale sizes of correspondence points; a correspondence point selecting unit that, based on the set of information about relative scale sizes of 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. a first local feature value generation unit that detects one or more of first feature points from a first image; outputs a set of first scale information, the set being made up of scale sizes of each of the first feature points; generates first local feature values of a region of a preset range encompassing each of the first feature points; and outputs a set of information about first local feature values, the set being made up of the first local feature values; a second local feature value generation unit that detects one or more of second feature points from a second image; outputs a set of second scale information, the set being made up of scale sizes of each of the second feature points; generates second local feature values of a region of a preset range encompassing each of the second feature points; and outputs a set of information about second local feature values, the set being made up of the second local feature values; a correspondence point calculation unit that calculates, as information about correspondence point(s), a correspondence relation between the first feature point(s) and the second feature point(s) based on the set of information about first local feature values and the set of information about second local feature values; and outputs a set of information about correspondence points, the set being made up of the information about correspondence point(s); 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 first scale information, the set of second scale information and the set of information about correspondence points; and outputs a set of information about relative scale sizes of correspondence points, the set being made up of the information about relative scale sizes of correspondence points; a correspondence point selecting unit that, based on the set of information about relative scale sizes of 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.