1. A photographic subject tracking device, comprising: a memory that stores instructions; and a processor that executes the instructions stored in the memory to: set a search area in an input image; calculate a first degree of similarity between a template image for tracking and an image in the search area; identify a tracked photographic subject position in the input image based on the first degree of similarity; calculate a second degree of similarity between each of multiple template images for resizing determination, which are generated based on the template image for tracking, and the image in the search area; identify matching positions of the multiple template images for resizing determination, respectively, in the input image based on second degrees of similarity; and change an image size of the template image for tracking and the template images for resizing determination based on a density of the plurality of matching positions.