1. An image processing apparatus which combines two images by superposing one on another, comprising: a reduced image generation unit configured to generate reduced images from original images to be superposed one on the other; an expectation value map generation unit configured to calculate feature values for each pixel of an original image of an image to be superposed, using a certain operator filter operating on pixels of the original images, to divide feature values of each pixel into blocks corresponding to the resolution of the reduced image, and to generate an expectation value map in which an expectation value of a feature value is registered; a feature point extraction unit configured to extract a feature point from the expectation value registered in the expectation value map; and a superposition unit configured to superpose one of a plurality of reduced images of original images to be superposed on another of the plurality of the reduced images using the feature points, to extract a feature point in an original image corresponding to the feature point from a result of the superposition, and to superpose the original images one on the other, wherein the feature point extraction unit removes an area in which it is determined that an object in an image is moving, and a feature point is extracted.