由於數位技術的進步，傳統的類比資料轉為數位格式儲存，不論是收藏或是攜帶都更為便利；網際網路的發達，也促進了數位資料的普及；此外，多媒體編碼技術的進步，數位資料所需的容量越來越小，對於上述的網路傳輸與儲存也變得更為方便。 然而，數位資料所遇到的問題也接踵而來。由於數位資料易於複製的特性，使用者可以輕易的對其複製散播，使得創作者的智慧財產權受損。更甚者，利用偽造、變更、剪接等方式，對其內容更改，破壞原先內容的含義，進而做為己用。以監視系統為例，數位監視影像因為內容易於更改的特性，大幅降低了影像的公信力與可靠性。因此，我們提出了一個完善的數位浮水印機制，對於數位影像的內容加以驗證，由萃取出的浮水印，可判斷數位影像內容是否遭受竄改、加入畫面、移除畫面或是畫面調換等剪輯攻擊。 我們以區塊DC值做為畫面之特徵，利用畫面內容分析的方式，判斷畫面場景切換以及影像雜湊值，再由場景內之畫面內容與單一畫面的雜湊值做為浮水印序列的生成參數，利用人類視覺模組依據畫面適應性地調整浮水印能量，在不破壞畫面品質下，盡可能地增強浮水印的強健性。 利用我們所提出的浮水印方法，嵌入的浮水印將顯示影像畫面或片段的順序，因此任何企圖更改影像片段順序或是以刪除或插入畫面來改變視訊內容的攻擊都將被偵測出來。此外，本研究方法不但能在維持原始影像品質下，對影像內容做有效的驗證，還能夠抵抗重新壓縮等攻擊。我們相信本研究所提出之H.264/AVC視訊壓縮與數位浮水印整合機制，將對建立更完美的多媒體資訊架構作出貢獻。 Digital contents have become increasingly popular nowadays due to their convenience of transferring and storage. In addition, the rapid growth of broadband networks and advanced coding technologies make creation and distribution of digital contents much easier and faster than ever. However, digital contents can be easily modified and the malicious tampering of data may change the meaning of contents. In this research, we propose a digital watermarking scheme under the framework of H.264/AVC. The watermark is embedded into video frames to ensure the correct frame order. Such attacks as frame dropping, swapping or insertion can be reflected from the unambiguous watermark detection. We use DC values of blocks as the features of the image, which can help determine whether a shot change occurs. The image hash value is calculated by content analysis and used to generate the watermark sequence. The watermarking scheme uses a human perceptual model to adjust the watermark energy so that the watermark robustness can be enhanced without degrading the visual quality. By integrating the watermarking approach with H.264/AVC, we can make the watermark embedding/detection be done in a very efficient manner. The content-analysis mechanism not only makes the watermark imperceptible but simplifies the watermark detection process. The experimental results show that the embedded watermark can survive transcoding processes such as changing quality parameters or the coding structure. Besides, the frame modification attacks will be revealed by the successful watermark extraction.
