數位多媒體壓縮技術純熟與網路的快速發展使得數位化的影像、視訊等多媒體資料兼顧高品質與體積小，並且對於多媒體的發佈變也便的容易許多。由於數位多媒體資料易於編輯與複製的特性，使得數位化的資料易受竄改，使得多媒體資料的真實性（autnetity）與完整性（intergrity）受到質疑。多媒體的驗證主要目的為了確保數位多媒體資料的完整性與真實性避免受到竄改。在本篇論文中，提出一個以數位簽章為基礎的強健的影像/視訊驗證系統。主要透過量化編碼的方式取得區塊內容特徵的擷取形成驗證碼，再經由壓縮加密隨著影像/視訊傳送或儲存。對於惡意的竄改發出警告，其利用畫面資訊的區域性標示出竄改區塊；而對於影像/視訊的有損壓縮，像是JPEG、H.264/AVC等類型的合法操作，均能夠通過我們的驗證系統。更提出在H.264/AVC的監視系統下的改良方法，使我們系統產生的驗證碼長度小與提升驗證的效率，且不會影響驗證的準確率。 The creation and distribution of digital contents have become increasingly convenient these days thanks to the rapid growth of digital signal processing techniques and broadband networking infrastructure. Editing digital images/videos, which was thought to be only achievable by professionals, can now be done with inexpensive and widely available software and hardware. A content authentication scheme for digital images and videos is proposed in this research. In order to avoid the content from being unnoticeably tampered by using digital editing facilities, reliable visual features are extracted as the authentication code and transmitted along with the images and videos. The integrity of content in a picture or a frame can thus be guaranteed by comparing the similarity between the transmitted authentication code and the extracted feature. The features are sensitive to malicious modification of data but are resilient to allowed lossy compression. 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. Experimental results show the feasibility of the proposed algorithm.
