A plurality of block pairs are set by setting two of the rectangular blocks contained in one template as one block pair. A score showing a degree to which a part of an object is included in the template is held based on a relation of a relative level between block luminance values in each of the block pairs set in the template. These processes are carried out for all templates. Based on a sum of the scores of all the templates, and whether the object is included in the image is determined.