1. An information embedding apparatus comprising: an image obtaining unit to obtain image information; a first-information obtaining unit to obtain first information to be embedded in the image information obtained by the image obtaining unit; a second-information obtaining unit to obtain second information to be embedded in the image information obtained by the image obtaining unit, the second information having a higher degree of importance than that of the first information; a generating unit to generate watermark image information including a group of first image patterns including the first information and representing one bit or a plurality of bits and a group of second image patterns including the second information by using a dot size enlarged from the first image patterns; and a superposing unit to superpose the watermark image information on the image information obtained by the image obtaining unit thereby obtaining watermark-superposed image information.