臺灣博碩士論文加值系統

由於數位科技的進步，數位影像可能會被非法複製，甚至是竄改。因此，發展數位影像版權保護的方法是很重要的課題。在本論文中，針對這個目的，我們提出了數種數位浮水印的技術。數位浮水印必須具有強韌性來抵抗非法使用者對影像的各種操作。針對彩色影像，我們提出了四種方法分別來抵抗不同的攻擊。首先，利用在離散富利葉轉換頻域上產生環狀和對稱的峰值來抵抗旋轉和縮放的攻擊。第二，應用離散富利葉轉換和離散餘弦轉換兩個頻域來抵抗旋轉和裁切的攻擊。第三，我們提出了一種在離散富利葉轉換頻域上，利用一個組合函數來對峰值位置作編碼，此方法可用來抵抗影像列印和再掃描成數位影像的操作。第四，是利用一種重新縮放影像的技術來抵抗縮放和行列移除的攻擊。最後，我們也提出一種彩色影像驗證的方法，來證明影像的真實性和完整性。藉由檢查藏入影像中的驗證信號，我們可以指出影像被竄改之處。利用藏入驗證信號來作影像驗證的方法，可以不用另外存有一個影像特徵資料。相關的實驗結果證明所提方法是可行性的。

Due to the advance of digital techniques, digital images may be copied or tampered with illegally. Therefore, it is important to develop methods to protect the copyright of digital images and verify their integrity. In this study, digital watermarking techniques for such purposes are proposed. In addition, the watermark must have an ability of robustness because users may apply various operations on a watermarked image. For color images, four methods are proposed to handle different attacks. First, a method based on creating peaks circularly and symmetrically in the DFT domain is proposed to resist rotation and scaling attacks. Second, a watermarking method utilizing the DFT and DCT domains is proposed to survive rotation and cropping attacks. Third, a method based on coding peaks by a combinatorial function in the DFT domain is proposed to work against print-and-scan operations. Fourth, a method based on an image rescaling technique is proposed to resist scaling and line-removal attacks. Finally, an authentication method for verifying the fidelity and integrity of color images is also proposed, which uses a key to generate authentication signals randomly. By checking authentication signals in an image, tampered parts can be pointed out. Such authentication signals can be used to conduct the authentication work without using other signature data. Good experimental results prove the feasibility of the proposed methods.

ABSTRACT (in Chinese) i
ABSTRACT (in English) ii
ACKNOWLEDGEMENTS iii
CONTENTS iv
LIST OF FIGURES vii
LIST OF TABLES x

Chapter 1 Introduction 1
1.1 Motivation 1
1.2 Review of Related Works 2
1.2.1 Digital Watermarking against Geometric Attacks 2
1.2.2 Digital Watermarking against Print-And-Scan Attacks 3
1.2.3 Digital Image Authentication 4
1.3 Overview of Proposed Methods 4
1.3.1 Definitions of Terms 4
1.3.2 Brief Descriptions of Proposed Methods 5
1.4 Thesis Organization 11
Chapter 2 Copyright Protection by Watermarking for Color Images against Rotation and Scaling Attacks Using Peak Detection and Synchronization in DFT Domain 13
2.1 Introduction 13
2.2 Ideas of Proposed Method 14
2.2.1 Properties of Coefficients in the DFT Domain 14
2.2.2 Properties of Color Channels 16
2.2.3 Proposed Technique for Coding Peak Locations for Watermarking 17
2.2.4 Proposed Technique for Synchronizing Peak Locations for Protection against Rotation and Scaling Attacks 19
2.3 Watermark Embedding Process 20
2.3.1 Embedding of Watermarks 20
2.3.2 Detailed Algorithm 21
2.4 Watermark Extraction Process 24
2.4.1 Extraction of Watermarks 24
2.4.2 Detailed Algorithm 25
2.5 Experimental Results 28
2.6 Discussions And Summary 32
Chapter 3 Copyright Protection by Watermarking for Color Images against Rotation And Cropping Attacks Using Synchronization of Peak Locations in DFT Domain And Coefficient Relationship Comparison in DCT Domain 34
3.1 Introduction 35
3.1.1 Problem Definition 35
3.1.2 Review of Employed Techniques 36
3.2 Ideas of Proposed Method 37
3.2.1 Proposed Technique for Multiply Embedding Watermark in DCT domain for Preventing Cropping Attack 38
3.2.2 Proposed Technique for Hiding Verification Code in DCT Domain for Watermark Existence Check 39
3.2.3 Proposed Technique for Hiding Synchronization Peak in DFT Domain to Detect Rotated Angle 40
3.3 Watermark Embedding Process 40
3.3.1 Embedding of Watermarks 41
3.3.2 Detailed Algorithm 42
3.4 Watermark Extraction Process 43
3.4.1 Extraction of Watermarks 43
3.4.2 Detailed Algorithm 45
3.5 Experimental Results 48
3.6 Discussions And Summary 51
Chapter 4 Copyright Protection by Watermarking for Color Images against Print-and-Scan Operations Using Coding and Synchronization of Peak Locations in DFT Domain 53
4.1 Introduction 53
4.1.1 Properties of Images Applied Print-and-Scan Operations 54
4.1.2 Problem Definition 54
4.2 Ideas of Proposed Method 55
4.2.1 Proposed Technique for Coding Peak Locations for Watermarking 55
4.2.2 Proposed Technique for Automatically Adjusting Threshold Value for Extracting Watermark 56
4.3 Watermark Embedding Process 57
4.3.1 Embedding of Watermarks 57
4.3.2 Detailed Algorithm 58
4.4 Watermark Extraction Process 59
4.4.1 Extraction of Watermarks 61
4.4.2 Detailed Algorithm 62
4.5 Experimental Results 63
4.6 Discussions And Summary 67
Chapter 5 Copyright Protection by Watermarking for Color Images against Scaling And Line-Removal Attacks Using An Image Rescaling Technique 69
5.1 Introduction 69
5.1.1 Review of Employed Techniques 70
5.1.2 Problem Definition 70
5.2 Brief Description of Proposed Idea for Rescaling Technique 71
5.3 Watermark Embedding Process 72
5.3.1 Embedding of Watermarks 72
5.3.2 Detailed Algorithm 73
5.4 Watermark Extraction Process 75
5.4.1 Extraction of Watermarks 75
5.4.2 Detailed Algorithm 75
5.5 Experimental Results 79
5.6 Discussions And Summary 84
Chapter 6 Tampering Detection in Color Images by Signature-Free Authentication Using DCT-Coefficient Relationship Comparison 85
6.1 Introduction 85
6.1.1 Motivation 86
6.1.2 Problem Definition 86
6.2 Proposed Authentication Method 86
6.2.1 Semi-Fragile Watermark Embedding Process 87
6.2.2 Image Authentication Process 89
6.3 Experimental Results 92
6.4 Discussions And Summary 97
Chapter 7 Conclusions and Suggestions for Future Works 99
7.1 Conclusions 99
7.2 Suggestions for Future Works 102
References 103

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