1. An imaging device for tracking moving objects, comprising: an image output device configured to output image data including a first image obtained at a first time and a second image obtained at a second time subsequent to the first time; a memory device configured to store the image data output by the image output device; and an image processing device including a local storage unit and configured to perform a block matching processing on the first image and the second image to track an object in the first and second images, wherein the block matching processing comprises: evaluating a feature value of a first image block in the first image and storing the feature value for the first image block in the local storage unit, dividing the second image into a plurality of divided regions; storing image data of a first divided region of the plurality of divided regions in the local storage unit; determining a similarity of the first image block to image blocks in the first divided region and storing results of the similarity determination in the local storage unit; storing image data of a second divided region of the plurality of divided regions in the local storage unit by overwriting the stored image data of the first divided region; determining a similarity of the first image block to image blocks in the image data of the second divided region and storing results of the similarity determination in the local storage unit; and determining similarity of the first image and second image according to results of the similarity determination for each of the plurality of divided regions stored in the local storage unit.