An image processing method corrects an image acquired from a medium exposed to ultraviolet light and makes parts printed with UV ink easily recognizable. A control device acquires a first image captured by an image sensor from a check exposed to visible light, and acquires a second image captured by the image sensor from the check when exposed to ultraviolet light. The control device generates a first edge image by applying an image processing filter that extracts edges in the first image, and generates a second edge image by applying an image processing filter that extracts edges in the second image. The control device then finds common edges where a first edge extracted in the first edge image and a second edge extracted in the second edge match each other, removes the common edges from the second edge image, and outputs a second image from which the common edges are removed.