數位科技的快速發展與先進的資料壓縮技術讓視訊資料的儲存與傳輸變得更為便捷，數位攝影機已經取代了傳統類比式錄影設備而廣泛運用於各種應用中。然而，數位資料易於編修的特性卻使其真實性受到若干質疑。在視訊資料中，片段的插入、刪除、更換或互換是最常見也最容易施行的攻擊方式，這樣的攻擊可在不被察覺的情形下改變資料的內容。本研究針對此類攻擊提出一個基於數位浮水印之視訊內容驗證機制，我們透過數位浮水印的嵌入與正確的偵測與驗證，來確認該視訊的內容順序。在本機制中，數位浮水印在視訊資料被壓縮的過程中被嵌入而在解壓縮的過程中被偵測以增加運算效率。H.264/AVC優異的編碼效能使其被廣泛地運用於多種場合，我們因此選擇將數位浮水印機制建構於H.264/AVC之上。 為了達成浮水印有效嵌入與偵測，以及避免檔案大小的增加，我們將浮水印訊號嵌入於非零的量化係數上，而數位浮水印資訊則包含了影片片段的序號。為了避免浮水印的嵌入造成影片畫質下降，我們根據Watson's視訊模型中的亮度遮罩(luminance masking)來調整浮水印的能量，在不影響人眼視覺的情況下增加浮水印的強健度。此外，我們也偵測場景轉換畫面以其產生能夠適度抵抗失真壓縮的雜湊數，再利用此雜湊數產生擾亂浮水印的序列，一方面可以達到浮水印嵌入和偵測的同步，另一方面也增加了浮水印的安全性。在論文中我們對浮水印嵌入與偵測的方式做深入討論，以期確實能實作於H.264/AVC中，並達成預期目標。實驗結果顯示藉由數位浮水印的方式可協助驗證數位影片的完整性與真實性。 Digitization of videos brings a lot of convenience to the transmission and archiving of visual data. However, the ease of manipulation of digital videos gives rise to some concerns about their authenticity, especially when digital videos are employed in the applications of surveillance. In this research, we try to tackle this problem by using the digital watermarking techniques. A practical digital video watermarking scheme for authenticating the H.264/AVC compressed videos is proposed to ensure their correct content order. The watermark signals, which represent the serial numbers of video segments, are embedded into nonzero quantization indices of frames to achieve both the effectiveness of watermarking and the compact data size. The human visual characteristics are taken into account to guarantee the imperceptibility of watermark signals and to attain an efficient implementation in H.264/AVC. The issues of synchronized watermark detections are settled by selecting the shot-change frames for calculating the distortion-resilient hash, which helps to determine the watermark sequence. The experimental results demonstrate the feasibility of the proposed scheme as the embedded watermarks can survive the allowed transcoding processes while the edited segments in the tampered video can be located.
