1. An image processing device that performs image processing on a composite image obtained by merging a first image and a second image having different exposure conditions, the image processing device comprising: a data acquiring unit that acquires the composite image and region data indicating a target region of the composite image; and an image processing unit that performs different image processes between the target region and a region other than the target region based on the region data, wherein the first image and the second image include a region on which a moving subject is rendered, the composite image is generated by using a pixel value of one of the first image and the second image in the region on which the moving subject is rendered, and the region data represents one or a plurality of regions generated based on the region of the composite image, on which the moving subject is rendered, as the target region.