1. An image processing apparatus comprising: a selector, arranged to select a plurality of feature points on or near a contour line of a region of interest when a contour of the region of interest in a reference image sensed at reference time or viewpoint is input; a memory for storing a connectivity between the plurality of selected feature points; a seeker, arranged for seeking a plurality of corresponding points, which respectively correspond to the plurality of feature points, in an image to be sought, which is sensed at another time or viewpoint; and an extractor, arranged to extract a contour between the plurality of corresponding points as a region of interest of the image to be sought on the basis of the connectivity stored in said memory.