1. An object-tracking computer program product that stores a program, that is executed on a computer, for tracking motion of an object between images of a plurality of frames that are input in chronological order, the program executed by the computer comprising steps of: template matching, wherein template matching of each frame of an input image to a plurality of template images is performed, a template image having a highest similarity with an image within a predetermined region of the input image is selected as a selected template among the plurality of template images and the predetermined region of the input image is extracted as a matched region; object-tracking, wherein, with reference to an image within the matched region that is extracted in the step of template-matching, by tracking motion between frames, motion of an object is tracked between the images of the plurality of frames; determining as to whether or not a result of matching in the step of template-matching satisfies an update condition for updating the plurality of template images; and updating, in a case that the update condition is determined to be satisfied in the step of determining, at least one of the plurality of template images.