1. An image processor comprising: an acquisition unit that acquires a read-out image read out by an image reading apparatus; a detection unit that detects, from the read-out image acquired by the acquisition unit, an embedded image including a first specified image having a first shape and a second specified image having a second shape; an adding unit that adds attribute information to a specified region in the embedded image detected by the detection unit, in accordance with an appearance ratio of the first specified image in the specified region, and that adds attribute information to other region surrounding the specified region in the embedded image detected by the detection unit, in accordance with an appearance ratio of the first specified image in the other region; and a determination unit that determines whether or not the specified region is to be subjected to a predetermined processing using the first specified image on the basis of whether or not the attribute information added to the specified region corresponds to the attribute information added to the other region.