| Summary: | 碩士 === 國立成功大學 === 資訊工程學系碩博士班 === 90 === The enormous popularity and the explosive growth of the World Wide Web demonstrate the commercial potential of offering multimedia resources (such as image, audio, and video) through digital networks. Therefore, the security and copyright issues have become more and more important. Nowadays, it is not quite secure in the design of valuable media. Therefore, this also increases the possibility of making an unlimited number of unauthorized copies, which can seriously endanger the ownership rights. In order to solve above problem, the technology of cryptography, data hiding, copyright protection system for digital image, or digital watermarking become the focus of research. Although the technology of cryptography can overcome many security problems, it must be conquered in the authentication and verification problems for intellectual property right. In these copyright protection schemes, digital watermarking technology is the most common method recently.
The digital watermarking techniques mean that the legal owner embeds his/her watermark (such as trademark, logo, portrait) in the image, which is used to prove the ownership of this image. The watermark must survive standard image modifications (such as blurring, cropping, scaling, rotating, and sharpening) or lossy data compression (such as JPEG compression). Therefore, it can be proven who the legal owner is. It would be detected that the image was embezzled or forged by the illegal user.
The experimental results are presented in this thesis; they are shown that the Chang-Hwang-Hwang scheme is insecure. In order to improve the Chang-Hwang-Hwang watermarking scheme, we propose two copyright protection schemes for digital images. The property of these two copyright protection schemes is that the watermarked image is the same as the original host image. In other word, two protection schemes that they needn’t change the pixels for embedding the watermarks. Therefore, these two methods we proposed are called copyright protection technology for digital image. The basic concepts of these two copyright protection technology for digital image is to extract the characteristic of the image and combine it with the watermark (the copyright declaration) will be signed by a trusted third party (time-stamp signature). When the ownership of image is in dispute, the legal owner may employ the time-stamp signature and the watermark that is extract by the secret key. It can be proven who the legal owner is. In these two methods we proposed, they can be possible to retrieve the watermark after various image processes. If an attacker claims that he has the copyright for digital image held by legal owner, then he can’t retrieve the image of watermark clearly. Therefore, it can be identified this image is illegal. Further, the ownership of the image will be proven.
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