Adaptive watermarking for printed document authentication

The rapid growth in information and communication technologies provides ways for some people to forge printed documents. Digital watermarking is widely used for authenticating digital documents. By embedding some watermarks in the printed documents in a way not to be observed by human eyes we may stop these forgeries. While a printed document requires another procedure to extract the embedded watermark and this process normally suffers from image distortion which is made by either printer's quality or scanner's precision. In this paper, the proposed watermarking scheme is capable of authenticating the embedded watermark in the printed documents. There is a factor to regulate the amount of watermark to be embedded in each specified partition of the image known as regulation factor. In terms of security, the embedding process employs different values of regulation factor. As the watermarking scheme uses a matrix of regulation factors rather than a fixed regulation factor, it is considered as an adaptive embedding. On the other hand, once the watermarked document is printed, it is required to be scanned. The geometric distortion is required to be removed from the scanned document including watermark in order to improve the quality of the retrieved watermark so that the extracted watermark is normalized. By doing this, the extracted watermark is clearer for visual authentication.