1. An apparatus comprising: a determining unit that determines a compositing method of compositing an original document image, a copy-forgery-inhibited pattern image with both a latent-image part that clearly appears on a copy and a background-image part that gets paler than the latent-image part or disappears such that the latent-image part clearly appears on the copy, and a form image with pixels that conceal the copy-forgery-inhibited pattern image in a case where the form image is overlaid on the copy-forgery-inhibited pattern image in an area where both of the latent-image part and the background-image part of the copy-forgery-inhibited pattern image are overlaid; an original-document-attribute determining unit that determines an attribute of the original document image; a form-attribute determining unit that determines an attribute of the form image; and a compositing unit that performs sequence of compositing of the original document image, the copy-forgery-inhibited pattern image, and the form image, by the compositing method determined by the determining unit, wherein the determining unit determines the compositing method based on the determined attribute of the original document image and the determined attribute of the form image, the compositing method being one of: a first compositing method of compositing, in order from top to bottom, the original document image, the copy-forgery-inhibited pattern image and the form image, a second compositing method of compositing, in which the original document image is first overlaid on the form image, and then the copy-forgery-inhibited pattern image is overlaid on a resulting image, and a third compositing method of compositing, in which the form image is first overlaid on the copy-forgery-inhibited pattern image, and then the original document image is overlaid on a resulting image, and wherein the determining unit determines: the first compositing method of compositing when the determined attribute of the original document image is not the primary attribute and when the determined attribute of the form image is the primary attribute, the second compositing method of compositing when the determined attribute of the original document image is the primary attribute, and the third compositing method of compositing when the determined attribute of the original document is not the primary attribute and when the determined attribute of the form image is not the primary attribute.