高容量JPEG資訊隱藏及其在影像分享、驗證與修復之應用

Abstract

本論文基於Joint Photographic Experts Group (JPEG) 技術提出了資訊隱藏、影像分享、影像驗證與修復之方法。資訊隱藏是藉由將機密資料藏於掩護影像，使得攻擊者無法從偽裝影像中察覺出機密資料的存在，以達到保護機密資料的一種方式；然而，大部份資訊隱藏方法所產生的偽裝影像大小並不經濟。因此，將偽裝影像壓縮以節省儲存空間是必要的，但壓縮經常會破壞藏於偽裝影像的機密資料。為了解決這個問題，我們提出了一個高容量可逆式JPEG資訊隱藏方法。這個方法將機密資料藏於JPEG壓縮碼。在機密資料被無失真取出後，原來用於藏機密資料的JPEG壓縮碼，也可以完整重建回來。 機密影像分享藉由將機密影像產生n張有雜訊的分存來保護機密影像。任意k份分存 (2 □ k □ n)，可以還原機密影像，但少於k份分存，則無法還原機密影像。這種性質(不是機密影像被還原就是只有雜訊)，只有當被分享的影像為最高機密才有用處；然而，在真實世界中，並不是所有的影像都為最高機密，分享的影像有可能是每天需要處理的重要影像，而不是最高機密影像。因此，還原重要影像可能會涉及到某些品質層次。為了可以根據收集分存的數量多寡，來還原重要影像的多種品質，我們提出了一個漸進式影像分享方法。這個方法所產生的每個分存都非常的小，所以這些小分存可以成功地藏於JPEG壓縮碼，使得這些隱藏於JPEG壓縮碼下的小分存在一個不友善的環境傳送時，可以減低被攻擊的機率。 影像驗證是用來檢驗影像的完整性。有些具有自我修復能力的影像驗證方法除了可以偵測影像是否遭到惡意竄改，而且在影像被偵測遭到竄改時，也可進而修復；然而，當影像遭到更嚴重破壞時，所遺留的修復資料並不足以用來修復。因此，我們提出了一個影像驗證與交叉修復方法來保護一組n張JPEG影像。這個方法可以檢驗該組n張JPEG影像有哪幾張被竄改，而且還可以藉由其它未被竄改的JPEG影像之間的相互合作來修復被竄改的JPEG影像。

This dissertation proposes three techniques for data hiding, image sharing, and image authentication with cross recovery based on Joint Photographic Experts Group (JPEG). Data hiding is used to protect secret data by embedding them in a cover image such that attackers cannot identify a hidden secret in the stego-image. However, the stego-images generated by many existing data hiding techniques are not economic in size, and therefore the compression to the stego-images is needed to reduce storage space. Unfortunately, the compression usually destroys the hidden secret in the stego-images. To solve this dilemma, a reversible JPEG data hiding method with high hiding capacity is proposed. The secret data are embedded in a JPEG code. In the decoding process, following lossless extraction of the hidden secret data, the JPEG code used to embed the secret data can also be reconstructed without any error. Secret image sharing is used to protect a secret image by splitting the secret image into n noise-like shadows. Any k of the n shadows can reconstruct the secret image, but fewer than k shadows cannot. This all-or-nothing property is useful when the image being shared is top secret. However, in the real world, not all images are top secret. The shared image might be a daily-used important image but not a top-secret one, and therefore the reconstruction of the important image can involve certain quality levels. To reconstruct the important image with various quality levels based on the number of collected shadows, a progressive image sharing method with compact shadows is proposed. All n shadows are very compact, and so can be hidden successfully in the JPEG codes of cover images to reduce the probability of being attacked when transmitted in an unfriendly environment. Image authentication is used to verify the integrity of an image. Some Image authentication schemes with self-recovery ability not only identify unauthorized manipulations of the image but also recover the tampered areas with approximation of the original ones. However, when the image is seriously damaged, the recovery data left are insufficient to recover the the seriously damaged image. Therefore, an image authentication and cross-recovery method is proposed to protect a group of n JPEG image. The proposed method can verify which JPEG images in the group are tampered with, and recover the tampered JPEG images approximately through the cooperation of the survived members.