1. An object tracking apparatus for tracking an object included in images provided successively, the object tracking apparatus comprising: a first registering unit configured to register a partial image indicating an object in a predetermined image among the provided images as a template; a first matching unit configured to estimate a first object region by matching another image of the provided images with the template registered by the first registering unit; a second registering unit configured to register a histogram generated based on a pixel value of the partial image indicating the object in the predetermined image among the provided images; a second matching unit configured to estimate a second object region by matching a histogram of a partial region of the another image with the histogram registered by the second registering unit; and an object region determination unit configured to determine, based on estimation results of the first matching unit and the second matching unit, an estimated object region by employing the estimation result of either one of the first matching unit and the second matching unit, wherein in a case where a distance between the second object region and the first object region is within a predetermined range, the object region determination unit determines the first object region as the estimated object region, and wherein in a case where the distance between the second object region and the first object region is not within the predetermined range, the object region determination unit determines the second object region as the estimated object region.