摘要 網路的快速發展以及先進的影像/視訊壓縮技術，為高品質數位媒體的發佈帶來許多便利，然而數位化多媒體也具有容易複製、存取與修改的特性。因此，多媒體資料的驗證即判斷多媒體資料的真實(authentity)與完整性(integrity)將變得更加重要。在本篇論文中，我們將現有的驗證技術與挑戰作討論，並且提出符合現今使用環境的驗證系統。此多媒體驗證技術利用畫面資訊的區域性(localization)指出影像畫面中可能遭受竄改的部份，並且抵抗影像/視訊壓縮所造成的影響。 對於畫面竄改的認定，我們以畫面內容意義改變與否作為惡意竄改的定義。有別於以往的多媒體驗證系統，我們所提出的影像/視訊驗證技術是以向量量化(Vector Quantization)為基礎，利用影像/視訊壓縮格式中既有的DCT係數區塊取出DC係數值，作為日後驗證的依據，接著透過簡單的區塊分類，將分別是具有資訊的區塊或者平滑的均勻區塊經由不同向量量化方法來達到影像內容驗證的目的。實驗顯示這樣的方法可適用於靜態影像JPEG壓縮與H.264等之視訊壓縮格式。 Video/Image Authentication by Vector Quantization The rapid growth of signal processing techniques and widespread networking facilities make creation and distribution of digital contents much easier and faster than ever. Users nowadays can produce images/videos with their low-cost software and hardware and then transmit and share the digital data with others by using broadband networks. The convenience brought by the digital technology definitely benefits most of the content users but certain concerns may arise. One challenging issue is related to content authentication of digital images/videos. Many surveillance cameras store data in digital formats to facilitate their storage and transmission. However, the ease of editing digital data may void their effectiveness as evidence or a proof on the court. Thus, the authenticity of digital images/videos should be further ensured so that they can serve as reliable evidence without doubt. In this thesis, a content authentication scheme for digital images and videos is proposed. The classified vector quantization of image/frame blocks is employed to create a digital digest or an authentication code, which is less sensitive to the lossy compression process and will be transmitted with the images/videos. The receiver can calculate the similarity between the transmitted digest and the extracted one to determine if the content has been tampered. The tampered region can even be located to help identify the motivation of the attacker. The proposed scheme is closely tied with H.264 video codec to achieve better efficiency. Issues about codebook design and security are also discussed thoroughly. Experimental results show the feasibility of the proposed scheme.