1. An image processing apparatus comprising: a layer separating unit configured to separate an input frame image data item into a moving subject layer and a background layer; and a combining processing unit configured to generate a combined image data item by performing an image combining process using the input frame image data item; wherein, in the image combining process, top priority is given to a moving subject layer of the latest input frame image data item, a second priority is given to a moving subject layer of a frame image data item associated with a previously performed combining process, and a layer-image combining process is performed for a partial area of an existing combined image data item.