1. An image reader comprising: a reading unit that reads an image; a detection unit that detects marks from the read image read by the reading unit; a creation unit that creates a hiding image, which hides a region including the marks, on the basis of the marks detected by the detection unit; and a combining unit that combines the read image and the hiding image to create an electronic document, the creation unit further creating a display image for displaying a hidden image, which is present in a region hidden by the hiding image, in a different region from the hiding image.