Printed Document Watermarking Using Phase Modulation

This paper describes printed document watermarking for the authentication. The hidden information is in the form of two dimensional binary images. It can be of any shape and can be printed on any part of a document. The phase modulation is the technique to hide this binary image as a watermark into the image. This hidden information becomes visible to the human eyes only when a correct decoder is positioned on the top of this optical watermark with the right alignment. Thus, with such a "modulate and demodulate" approach, it secures printed document. In this paper carrier dot array structure is designed which can be modulated by changing the inter pixel distances i.e. phase of the grid. The work is carried out on the test images to decide this phase value.