利用可移除之可視浮水印技術作影像版權保護及驗證

Abstract

由於數位科技的發展，數位影像可能被複製，甚至被竄改。這將會引起非授權者對數位影像的非法使用。因此，可利用數位浮水印技術來證明影像的版權。然而，使用者往往需要同時保存原始影像及其加入浮水印的影像，這將會造成儲存空間的浪費。因此，嵌入可移除可視浮水印的方法是非常值得發展的。在這篇論文裡，我們提出三種嵌入可移除可視浮水印的方法。首先，針對BMP影像，利用人類視覺模型及替換LSB的方法。接著，根據排序調色盤的方法來處理GIF影像。最後，調整DC係數值的方法來處理JPEG影像。在我們所提出的方法中，皆可透過移除嵌入的可視浮水印來恢復原始影像，並且，我們可藉由抽取可視浮水印來證明影像版權。此外，對於BMP和GIF影像，我們所提出的方法也可驗證其影像的完整性。相關的實驗結果證明所提方法的可行性。最後，我們也提出一個具雙層架構概念的影像認證機制，其相關的服務則由區域與中央影像認證中心提供。

Because of the development of digital technologies, digital images may be copied or even tampered. This will result in unauthorized uses, misappropriation, and misrepresentation of digital images. Digital watermarking techniques are used for verifying the copyright of images. However, users need to keep both original images and corresponding watermarked ones. This really results in a waste of storage space. Consequently, a method of embedding removable visible watermarks is quite worthy to develop. In this study, three methods are proposed for this purpose. First, a method using a human visual model and the LSB replacement technique is proposed for BMP images. Next, a method based on a sorted color palette is proposed for GIF images. Lastly, a method based on the adjustments of DC DCT coefficient values is proposed for JPEG images. All of the proposed methods can be employed to remove embedded visible watermarks to restore original images. The copyright of the watermarked image can be verified by the three proposed methods by extracting the embedded visible watermark. Moreover, for BMP and GIF images, the integrity of an image can also be authenticated by the proposed methods. Good experimental results prove the feasibility of the proposed methods. Finally, a concept of two-level image authentication mechanism is also proposed, based on which some functions of local and centralized image authentication centers are suggested.