1. An image processing device, comprising: an identifying unit, implemented by a processor, that identifies a first image area including a first plurality of pixels or a second image area including a second plurality of pixels, in a first captured image obtained by capturing a subject image, a first luminance value of each of the first plurality of pixels being equal to or less than a first threshold value and a second luminance value of each of the second plurality of pixels each being equal to or greater than a second threshold value; an image texture image generation unit, implemented by the processor, 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; an interpolation unit, implemented by the processor, 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; and a threshold value setting unit, implemented by the processor, that alters at least one of the first threshold value and second threshold value based upon luminance information of the first captured image.