臺灣博碩士論文加值系統

多數的數位影像認證系統都使用數位浮水印的技術來實現之，一般來說我們將數位浮水印技術分成：空間域浮水印及頻率域浮水印。空間域浮水印是相當脆弱的，容易受到非惡意人為破壞所影響，如常見之JPEG影像壓縮。所以越來越多的數位浮水印技術都轉移至頻率域浮水印，相較於空間域浮水印，無論是浮水印的彈性及強健度，頻率域浮水印都佔有相當之優勢，它可以避免浮水印過於脆弱而被一些合理的影像失真縮破壞，但是卻又能偵測出惡意的人為破壞行為。
本論文提出了一個新的影像認證系統，保障了影像內容及影像所有權，我們的影像認證系統使用了頻率域浮水印技術並結合了公開金鑰密碼學。我們使用頻率域離散餘弦轉換(DCT)之低頻係數作為我們的影像認證特徵，由此計算出影像不變量再利用DSA的簽章技術產生數位簽章，視之為數位浮水印後再使用了量化的技術嵌入至頻率域DCT中頻係數，達到任意第三人可以驗證影像但卻無法偽冒產生認證用浮水印的效果。在驗證影像的過程中我們不需要原始的影像來輔助，任意人都可以取的影像擁有者的公開金鑰進行驗證，從我們的實驗結果可以證實，我們的數位影像認證系統具備抵抗JPEG壓縮破壞的能力，且對於其他合理的影像失真如影像銳利化、模糊化等都有相當不錯之效果。同時可以透過認證的結果指出影像何處遭受到惡意的人為竄改。

Many digital image authentication techniques can be achieved by using digital watermarking scheme. Digital watermarking scheme is generally categorized into spatial domain and frequency domain bases. Spatial domain watermarking scheme is fragile and is hard to resist incidental distortion such as JPEG compression. Frequency domain watermarking scheme has better robustness than spatial domain watermarking scheme；it can stand reasonable distortion and detect illegal distortion through malicious tampering.
In this thesis, we proposed a new image authentication system which can preserve the integrity of image content and claim image ownership. Our proposed system is a frequency domain watermarking scheme with public-key cryptography. We compute feature value from invariable data in low-band DCT coefficients and provide an additional property of public verification by producing a DSA signature on the image feature we have found. We use quantization technique to embed our signature in the middle-band DCT coefficients. In verification steps, we do not need original image since we can retrieve the embedded watermark from received image. Everyone can authenticate the image but can not forge the owner’s signature. The experimental results show that, our image authentication system can adequately resist the incidental distortion like JPEG compression and resist the reasonable image distortion such as sharpening and blurring. Our system also can indicate the malicious tampering area when the image suffers from an illegal modification.

中文摘要 i
ABSTRACT ii
誌謝 iii
第一章 導論 1
1.1. 研究動機 1
1.2. 研究目的 2
1.3. 文獻回顧 3
1.4. 論文架構 5
第二章 數位影像認證技術 7
2.1. 公開金鑰密碼學與數位簽章 7
2.2. DSA數位簽章演算法 8
2.3. 數位浮水印技術 11
2.3.1. 數位浮水印之分類 11
2.4. 以數位浮水印為基礎的數位影像認證需求 14
2.5. 數位浮水印影像認證演算法 15
2.5.1. 數位浮水印產生方式 15
2.5.2. 浮水印嵌入方式及萃取方式 17
2.5.3. 安全上的挑戰 21
第三章 離散餘弦轉換與JPEG影像壓縮技術簡介 23
3.1. 離散餘弦轉換 23
3.1.1. DCT係數在頻率上的意義 24
3.1.2. DCT公式釋義 25
3.2. JPEG影像壓縮技術簡介 26
3.2.1. JPEG壓縮模式 27
3.2.2. JPEG壓縮基本流程 28
第四章 基於公開金鑰密碼學的高彈性影像認證系統 33
4.1. 脆弱的公開金鑰影像認證系統 33
4.2. 基於公開金鑰密碼學的高彈性影像認證系統 37
4.2.1. 方法概述 37
4.2.2. 擷取影像特徵值 39
4.2.3. 嵌入浮水印-使用量化技巧 42
4.2.4. 影像驗證 45
第五章 實驗結果與分析 48
5.1. 實作環境 48
5.2. 定義特徵量化表及嵌入量化表 49
5.2.1. 特徵量化表 49
5.2.2. 嵌入量化表 52
5.3. 影像失真評估工具 56
5.4. 浮水印影像PSNR評估 57
5.5. 抵抗JPEG壓縮能力測試 59
5.6. 惡意竄改測試 60
5.7. 影像失真測試 62
5.8. 實驗結果討論 63
5.9. 系統安全性討論 66
第六章 結論與未來展望 68
參考文獻 69

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