1. An electronic watermark embedding apparatus that embeds watermark information as digital information into a document image, the apparatus comprising: a background determining unit that determines whether pixels on the document image are pixels composing a background image; a background eliminating unit that eliminates the pixels determined as the pixels composing the background image by the background determining unit from the document image; and a watermark embedding unit that embeds a watermark into a background eliminated image from which the background is eliminated by the background eliminating unit.