A PC generating image data divides data to be embedded into a predetermined size and arranges it in a predetermined area of a watermarking image. In the predetermined area are defined positions a-h assumed by an information dot configuring an information pattern based on the data to be embedded, and, of positions a-h, a position defined for the information pattern is assumed by a point dot. Of positions a-h, a position that is not defined for the information pattern is assumed by a linear dot. Furthermore in the predetermined area there is a position assumed by a positioning dot defining the predetermined area, and this position is assumed by a point dot. The linear dot has a geometry extending in one of the main scanning direction and vertical scanning direction of an image formation apparatus that allows higher performance in reproducibility for a line.