1. A trajectory estimation method for estimating a trajectory of a subregion constituting all or part of a moving object in a video, said trajectory estimation method comprising: accepting images included in the video, the images being temporally sequential; generating subregions at hierarchical levels by performing hierarchical segmentation on each of the images accepted in said accepting such that a spatially larger subregion includes spatially smaller subregions, the spatially larger subregion and the spatially smaller subregions belonging to hierarchical levels different from each other; and estimating, as a representative trajectory, a trajectory, in the video, of a subregion included in a certain image, by searching for a subregion that is most similar to the subregion included in the certain image, across hierarchical levels in another image different from the certain image, wherein in said estimating, a predictive subregion which is a subregion predicted in said another image is generated by changing a shape of the subregion included in the certain image, and the representative trajectory is obtained by searching for the subregion that is the most similar to the predictive subregion, across the hierarchical levels in said another image.