An image processing device includes an input unit, a generation unit, a gain processing unit, a development processing unit, and a composition unit. The input unit receives input of a plurality of images having different exposures from one another. The generation unit generates gain information according to each of the plurality of images input through the input unit. The gain processing unit applies gain processing to each of the plurality of images based on the gain information generated by the generation unit. The development processing unit applies development processing to each of the plurality of images to which the gain processing has been applied by the gain processing unit. The composition unit composites the plurality of images to which the development processing has been applied by the development processing unit.