Watermarking based document authentication in Script format

In almost all document authentication systems based on watermarking technique, the document is considered as a binary image and a watermark signal is embedded into it. However, actually an important document is saved in document description (DD) file, such as portable document format (PDF) file, instead of the image file. Because generally DD file is more compact in size than image files, and the content of the document is not easy to be modified. However, recently some computer tools permit user to modify the contents of DD file, which brings a necessity to develop an efficient document authentication scheme. Considering it, in the proposed scheme, a watermark sequence is directly embedded into the DD file (Script file), modifying metrics of each characters of it. The experimental results show very good performance in the document authentication. Also the computer complexity of the proposed scheme is sufficiently low to apply in the practical situation.