1. An apparatus comprising: (a) an image processor configured (i) to calculate a 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 that correspond to each other, (ii) to calculate a statistic of a plurality of the calculated similarities, with respect to a plurality of the image pairs, and (iii) 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 calculated statistics; and (b) an exposure unit configured to expose a substrate to a pattern based on the position of the object region recognized by said image processor.