1. An image processing device, comprising: an identifying unit that identifies an image area where gradations are lost in a first captured image obtained by capturing a subject image; an image texture image generation unit that generates an image texture image by aligning a second captured image, obtained by capturing an image of a subject matching the subject of the first captured image, with the first captured image and extracting an image texture corresponding to the image area having been identified by the identifying unit; and an interpolation unit that executes interpolation for the image area in the first captured image by synthetically incorporating the image texture image having been generated by the image texture image generation unit with the first captured image.