1. An apparatus comprising: a first calculation unit to calculate similarity between first image data of a first partial region in object image data and reference image data with respect to each pair of a second partial region of the first image data and a third partial region of the reference image data corresponding to each other; a second calculation unit to calculate a statistic of a plurality of similarities calculated by said first calculation unit with respect to a plurality of the image pairs; and a recognition unit to recognize, as a position of an object region in the object image data, a position of the first partial region in the object image data which has the highest statistic of a plurality of the statistic calculated by said second calculation unit.