This image processing device comprises: a color image acquisition means that acquires color image data representing a color image of biological tissue; a lesion determination means that determines whether or not each pixel in the color image is a pixel of a lesion on the basis of the color image data; and a marking means that makes a mark indicating the position of the lesion on the color image on the basis of the determination result. The mark is a mark through which the color image in the background can be seen.
