運用還原機制在小波轉換為基礎之半易碎型數位 浮水印

Abstract

在資訊高度發展的今日，影像驗證系統廣泛地應用在數位影像財產權保護，以維護數位影像之完整性。本篇論文提出以離散小波轉換(discrete wavelet transform, DWT)為基礎之半易碎型浮水印影像驗證與還原演算法，透過影像驗證系統可以精確地將受到竄改的影像區塊標示出來，並可進一步加以還原竄改區塊的資訊。我們也透過實驗證實，本影像驗證還原演算法可以承受相當程度下的JPEG 壓縮及高斯雜訊處理 (additive white Gaussian noise, AWGN)，且能成功驗證出影像受竄改的部位，並加以還原。

本論文是小波轉換為基礎之影像竄改偵測演算法，利用小波轉換之特性，由低頻區資訊產生影像驗證浮水印，並根據人類視覺上特性將影像驗證浮水印及影像還原資訊加以嵌入到小波轉換之高頻區，藉此我們能夠抵抗非惡意性的影像處理攻擊，且能正確地檢測出惡意的影像竄改行為，也能維持影像品質在一定的水準之上。

Nowadays, image authentication systems are widely applied to ownership protection and tampering detection of digital images. The main concept for those image authentication systems is that minor modifications which do not change the content of the image preserve the authenticity of the image, whereas modifications which do modify the content render the image not authentic. In this paper, we propose an image tampering authentication and recovery scheme based on discrete wavelet transform (DWT). Our image authentication system is able to locate precisely any malicious alteration made to the image and restore the altered or destroyed regions in order to allow the user to know what was the original content of the manipulated areas. We also analyze the robustness to mild modification like JPEG compression and channel additive white Gaussian noise (AWGN) and fragility to malicious attack. This thesis is based on wavelet transformation image tampering detection scheme. By the property of discrete wavelet transform we generate the semi-fragile watermark from low-frequency band and embedding the watermark into the high-frequency band with Human Visual System(HVS). Then we can resist the mild modifications of digital image and be able to detect the malicious modifications precisely. The watermarked image still preserve high quality after embedding the semi-fragile watermark.