Subject tracking computer program product, subject tracking device and camera

A subject tracking computer program product containing a subject tracking program executed by a computer in order to track movement of a subject through a plurality of input images input in time series, wherein:

• the subject tracking program enables the computer to execute:
• a template matching step through which each input image is matched through template matching with a plurality of template images including a plurality of template images (magnification factor—varied template images) at various magnification factors and a plurality of template images (time-lagged template images) obtained at different time points, a template image among the plurality of template images achieving a highest level of similarity to an image within a specific area in the input image is selected as a chosen template image and the specific area in the input image is extracted as a match-up area;
• a decision step through which a decision is made as to whether or not matching results obtained through the template matching step satisfy an update condition for updating the plurality of template images;
• and
• an update step through which at least one of the plurality of template images is updated upon deciding through the decision step that the update condition is satisfied.