Text Watermarking for OOXML Format Documents Based on Color Transformation

Abstract

A robust text watermarking approach has been proposed in this paper, in which the watermarks are embedded into the text by the transformation of characters’ RGB-style color in the OOXML format document. To get high watermark embedding capacity, two bits of the watermarking information are embedded between every two characters. The initial text content of the document is not changed after the embedding because of the good characteristics of OOXML format and the subtle adjustment of characters’ color, which ensure the good imperceptibility of the watermarking method. Most attacks such as “copy”, “save as”, “insert” and “delete” operations can be resisted by the proposed approach, and the location of the “insert” and “delete” operations can be detected by redundant embedding of the watermarking information. The proposed approach can be applied to files in “docx” and “doc” format.