Hindawi Publishing Corporation Advances in Multimedia Volume 2012, Article ID 875759, 17 pages doi:10.1155/2012/875759 Research Article Robust Signature-Based Copyright Protection Scheme Using the Most Significant Gray-Scale Bits of the Image Mohammad Awrangjeb Cooperative Research Centre for Spatial Information, Department of Infrastructure Engineering, University of Melbourne, VIC 3010, Australia Correspondence should be addressed to Mohammad Awrangjeb, mawr@unimelb.edu.au Received 15 November 2011; Revised 2 March 2012; Accepted 27 March 2012 Academic Editor: Xian-Sheng Hua Copyright © 2012 Mohammad Awrangjeb. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The most significant bit - (MSB-) plane of an image is least likely to change by the most signal processing operations. This paper presents a novel multibit logo-based signature, using the most significant gray-scale bits, which is then used to develop an extremely simple but robust copyright protection scheme, where images along with their signatures are sent to a trusted third party when a dispute arises. Different ways of processing the MSB-plane before calculating the robust signature have been developed. This paper then presents an innovative classifier-based technique to test the robustness and uniqueness of any signature-based scheme. A new MSB-based attack, which would defeat our scheme most, has also been proposed. Experimental results have clearly demonstrated the superiority of the proposed scheme showing the high robustness of different MSB-based signatures over the existing signature- based schemes. 1. Introduction For last few years, we have been using electronic commerce that includes online and offline distribution of multimedia data like images, audios, and videos. However, digital multimedia files can be easily manipulated using commercial graphics tools. Duplicating digital files has become as simple as clicking a button. Since maintaining an exact or manipulated duplicate of any digital data is easier than before, the enforcement of copyright protection has become more imperative than ever. Although copyright laws are being applied against abusers in order to ensure secure electronic commerce, the current problems with copyright protection obstruct the rapid evolution of computer and communication networks. As a result, the enhancement and further development of digital copyright protection is in cen- tral to the development of future communication networks [1]. There may be three types of solutions to the copyright protection problem: cryptographic tools, digital watermark- ing techniques, and digital signature-based techniques. Cryptographic tools [2] can be used to encrypt a multimedia file using some secret key. The encrypted file is no more perceptually understandable and can be distributed to the users. Only the appropriate user that holds the secret key can decrypt and use this file. Such a technique while suitable for text documents is not suitable for multimedia data for the following two reasons. First, multimedia file size is much larger than that of text. Therefore, encrypting or decrypting a multimedia file is highly time consuming. Second, the encrypted media file is not useful in the public domain, for example, in the Internet. Because the encrypted file is not perceptually understandable and if the encrypted information is decrypted once, the information is no longer protected. However, the multimedia file provides an opportunity that the text document does not. That is, while no distortion is allowed in the signed text, some distortions are allowed in the signed multimedia file as long as it is perceptually similar to the original file. Digital watermarking techniques take the opportunity of the abovementioned property of the media file. They embed a watermark such as logos, seals, or sequence numbers, into the original image. The embedded watermark should survive against both malicious and nonmalicious attacks depending on the applications. Latter, the embedded information is