利用數位浮水印與影像驗證作影像版權保護及竄改偵測之研究

Abstract

由於數位科技的進步，數位影像可能會被非法複製，甚至是竄改。因此，發展數位影像版權保護的方法是很重要的課題。在本論文中，針對這個目的，我們提出了數種數位浮水印的技術。數位浮水印必須具有強韌性來抵抗非法使用者對影像的各種操作。針對彩色影像，我們提出了四種方法分別來抵抗不同的攻擊。首先，利用在離散富利葉轉換頻域上產生環狀和對稱的峰值來抵抗旋轉和縮放的攻擊。第二，應用離散富利葉轉換和離散餘弦轉換兩個頻域來抵抗旋轉和裁切的攻擊。第三，我們提出了一種在離散富利葉轉換頻域上，利用一個組合函數來對峰值位置作編碼，此方法可用來抵抗影像列印和再掃描成數位影像的操作。第四，是利用一種重新縮放影像的技術來抵抗縮放和行列移除的攻擊。最後，我們也提出一種彩色影像驗證的方法，來證明影像的真實性和完整性。藉由檢查藏入影像中的驗證信號，我們可以指出影像被竄改之處。利用藏入驗證信號來作影像驗證的方法，可以不用另外存有一個影像特徵資料。相關的實驗結果證明所提方法是可行性的。

Due to the advance of digital techniques, digital images may be copied or tampered with illegally. Therefore, it is important to develop methods to protect the copyright of digital images and verify their integrity. In this study, digital watermarking techniques for such purposes are proposed. In addition, the watermark must have an ability of robustness because users may apply various operations on a watermarked image. For color images, four methods are proposed to handle different attacks. First, a method based on creating peaks circularly and symmetrically in the DFT domain is proposed to resist rotation and scaling attacks. Second, a watermarking method utilizing the DFT and DCT domains is proposed to survive rotation and cropping attacks. Third, a method based on coding peaks by a combinatorial function in the DFT domain is proposed to work against print-and-scan operations. Fourth, a method based on an image rescaling technique is proposed to resist scaling and line-removal attacks. Finally, an authentication method for verifying the fidelity and integrity of color images is also proposed, which uses a key to generate authentication signals randomly. By checking authentication signals in an image, tampered parts can be pointed out. Such authentication signals can be used to conduct the authentication work without using other signature data. Good experimental results prove the feasibility of the proposed methods.