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.
Forgeries related with official printed documents can easily be performed with the aid of today's advanced electronic devices such as scanners and computers. The forged documents are usually undetectable by human eyes and it is with this regard that there is an urgent need to find solutions to the threat of counterfeiting of such documents. With watermarking technique, information that is used to determine the validity of printed document can be embedded in the document. The embedded information can be imperceptible to human eyes, thus the process of forgery is made harder for the attackers. To authenticate the owner of the document, the embedded watermark is extracted from the watermarked document. However, in the verification process the printed document may suffer from printing and scanning (PS) distortion and as such it is necessary to resolve the noise and unwanted rotation as well as any degradation made by printing and scanning. This study proposed a watermarking technique to address this issue.
Keywords -digital watermarking; information hiding and security; normalization; offline printed documentsI.
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