Patent ID: 7287284

Claim:
An information processing method for embedding additional information in document data, comprising: a document data input step of inputting document data that includes a character string; an additional information input step of inputting additional information; an image data input step of inputting image data as a background image; a first embedding step of embedding the additional information in the input background image data, using a first digital watermark method and a parameter defining a robustness, wherein the first digital watermark method embeds information in an image by changing a pixel value using the parameter defining the robustness, and wherein the parameter is determined so that, in a case where an original document, in which information has been embedded using the first digital watermark method, is copied by a copying machine, the embedded information cannot be detected in the copied document output from the copying machine; a second embedding step of embedding the additional information in the input document data, using a second digital watermark method, wherein the second digital watermark method embeds information in an image by changing a distance between characters in the image so that, in a case where an original document, in which information has been embedded using the second digital watermark method, is copied by a copying machine, the embedded information can be detected in the copied document output from the copying machine; a composition step of compositing the document data in which the additional information has been embedded in the second embedding step, as a foreground image, and the background image in which the additional information has been embedded in the first embedding step; and an output step of outputting the document data composed with the image data in the composition step.