1. A photographic subject tracking method comprising: calculating similarity levels of images input sequentially to a template image; determining a photographic subject position in each of the input images based upon the similarity levels; tracking the photographic subject position through the input images; judging whether reliability of the similarity level calculated for the photographic subject position is high or low; and changing ways of at least one of calculating the similarity levels, determining the photographic subject position and tracking the photographic subject position, if the reliability of the similarity level is judged to be low.