Patent ID: 7085399

Claim:
A watermark information embedding device comprising: a document image forming section for forming a document image in units of pages on the basis of document data; a watermark image forming section for forming a watermark image in which dot patterns of a plurality of types are regularly arranged, and classified information is assigned to at least one type of dot pattern; a watermarked image synthesizing section for overlapping the document image and the watermark image to form a watermarked document image, and a pattern deciding section for selecting a specific embedding pattern in which the dot patterns are arranged so as to reduce obscuring, by the document image, of the dot patterns to which classified information is assigned, wherein the pattern deciding section changes at least two embedding patterns of the dot patterns to temporarily arrange the dot patterns, wherein the pattern deciding section selects the embedding pattern depending on a valid number of dot patterns which can be detected even though the document image and the watermark image are overlapped, and wherein the pattern deciding section, with respect to the at least two embedding patterns which are temporarily arranged, calculates variances of the valid numbers of dot patterns and selects the embedding pattern having the minimum variance.