本論文旨在研究數位影像之版權保護(copyright protection)與內容驗證(content authentication)。本文首先提出一植基於視覺密碼(visual cryptography)之版權保護技術。有別於大多數傳統的版權保護方法藉由將浮水印直接嵌入影像中來達成其目的之餘，難免會對欲保護之影像造成程度不一的影像失真；本文所提之方法利用欲保護之影像的特徵與一事先定義好之視覺密碼編碼簿將二元浮水印(binary watermark)藏匿於兩張分享影像中，不需要修改到欲保護之影像的內容。因此，欲保護之影像的視覺品質能夠被完整的保留下來。本方法的另一項優點即是無論欲保護之影像的尺寸為何，任意大小的二元影像皆可作為識別影像版權用之浮水印。本方法的實驗結果顯示，即使受保護之影像在經過如JPEG壓縮、雜訊添加和各種濾波器等影像處理攻擊後，藏匿於分享影像中之浮水印仍然能夠成功地被顯現出來。為了進一步節省儲存視覺密碼編碼簿所需的額外儲存空間，本論文提出另一個植基於視覺密碼且不需要依賴任何視覺密碼編碼即可達成影像版權保護之技術。相較於現有之版權保護方法，此強化後之技術對於許多常見的影像處理攻擊具有更強韌之抵抗能力。另外，實驗結果也顯示，惡意攻擊者無法成功地偽造出合法的分享影像來企圖竄改或侵犯受保護之影像的版權，證明本方法具有高度的安全性。
為了確保數位影像之完整性(integrity)與正確性(authenticity)，各種以區塊為基礎之影像驗證方法已經被陸續地發表出來。一個有效的影像驗證方法，除了必須具有敏銳的竄改偵測(tamper detection)能力來抵擋任何可能的攻擊之外，同時也要能夠從受攻擊的影像中，精確地定位出有哪些內容已經被竄改。然而在現有方法之中，絕大多數不是無法同時達成此兩項條件，就是必須犧牲竄改定位(tamper localization)的準確度來增強其對各種如向量量化(vector quantization)等偽造攻擊(counterfeiting attack)的抵抗能力。為了解決此一缺失，本論文提出一植基於fuzzy c-means分群法之以區塊為基礎的影像驗證技術來偵測並定位出受保護的影像中受竄改之區塊位置。本方法利用fuzzy c-means分群法成功地破除了各區塊之間的獨立性，使其除了能有效地抵抗各種偽造攻擊之外，亦同時提供精確的竄改定位功能。
假使影像認證執行者在偽造影像中找出被竄改的影像內容後，能夠立即自行復原該內容，使復原後的影像具有與原始影像相似的品質，便可以節省重新傳輸該影像所需的額外頻寬，因此，發展具有竄改復原(tamper recovery)能力的影像認證技術在近年來逐漸成為學者們關注的焦點之一。本論文提出一兼具有竄改偵測與竄改復原功能的彩色影像認證技術，此項技術不但能夠成功地從偽造影像中偵測並定位出受竄改的區塊位置，且能進一步利用隱藏在其他區塊的回復資料，將被竄改過的區塊復原。此外，本論文亦設計一連串的偽造攻擊模擬來驗證此項技術之竄改偵測與竄改復原功能的可行性與可靠性。

This dissertation addresses copyright protection and content authentication for digital images. In this context, we first propose a copyright protection scheme based on visual cryptography (VC) technique. Unlike most of conventional copyright protection schemes embedding a watermark into a host image directly that inevitable causes some permanent distortion, the proposed scheme conceals a binary watermark to two shares, according to the features of the host image and a predefined VC codebook, without modifying any pixel value of the host image. Therefore, the visual quality of the host image can be completely retained. In addition, the proposed scheme can use a binary image of arbitrary size as the watermark regardless of the size of host images. It is shown that the hidden watermark can be successfully revealed by the proposed scheme, even if the visual quality of protected images has undergone severe attacks, e.g., JPEG compression, noise addition and filtering.
To further save the extra storage space required to store the codebook, another VC-based copyright protection scheme that conceals the watermark to two shares without resorting to any codebook is proposed. The enhanced scheme provides stronger robustness against several image processing operations when compared with the existing copyright protection schemes. Moreover, the experimental results demonstrate that it is difficult for malicious attackers to break the security of the proposed scheme.
To ensure the integrity and authenticity of digital images, a wide variety of block-wise authentication schemes have been proposed in the literature. An effective authentication scheme should provide sufficient robustness to thwart any possible attacks with accurate tamper localization accuracy. However, most of the existing schemes either fail to address this issue or sacrifice tamper localization accuracy to withstand counterfeiting attacks, such as vector quantization (VQ) attack. For this reason, a novel block-wise authentication scheme based on fuzzy c-means (FCM) clustering is proposed for securely verifying the integrity of digital images and for identifying tampered image blocks. The proposed scheme successfully utilizes the FCM clustering technique to solve the security problem related to independent block-wise authentication schemes and at the same time preserves superior tamper localization accuracy.
Furthermore, an image authentication scheme with tamper recovery capability is desirable, as it will save additional bandwidth to retransmit the original images if the authenticator can directly remedy the tampered ones. Accordingly, we propose a novel block-wise color image authentication scheme, which can not only detect and determine the locations where the tampering occurred, but also approximately recover the tampered blocks by the recovery data hidden in other blocks. To verify the validity of the proposed scheme, the tamper localization capability and tamper recovery capability of the scheme under different counterfeiting attacks are studied and quantified in this dissertation.

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