Abstract
With the popularity of cloud computing and social networks, more and more JPEG images are stored and distributed. Consequently, how to protect privacy and content in JPEG images has become an important issue. Although traditional encryption schemes can be employed, the file format of JPEG images is changed so that their usage may be affected. In this paper, a reversible visual transformation algorithm is proposed to protect content in JPEG images. Specifically, the DC coefficient in each user-selected block is modified, while the information required to recover it is reversibly hidden into AC coefficients. Then the signs of AC coefficients in the selected blocks are flipped and the blocks are further scrambled with a secret key. By embedding the location information of the selected blocks in a transformed image, the original image can be exactly recovered when needed. Besides, regions to be protected can be arbitrarily chosen without substantially affecting the rest of the image. The experimental results on a set of JPEG images validate the efficacy and reversibility of the proposed algorithm. In addition, good performance is achieved in terms of invisibility of the protected content, image quality, file size preservation and security.
Highlights
With the popularity of cloud computing and social networks, more and more images are stored and distributed on the web
The algorithms for privacy protection in JPEG images can be classified into two categories: (1) algorithms performed on bit stream (e.g., [2]), and (2) algorithms performed on the quantified Discrete Cosine Transform (DCT)
As the experimental results conducted in [24] show, hiding data in low-frequency coefficients helps to achieve a smaller file size, and the 3rd to 11th AC coefficients of each block are chosen to carry the bit values
Summary
With the popularity of cloud computing and social networks, more and more images are stored and distributed on the web. Reversible data hiding (RDH) (e.g., [14]) is applied in Joshi’s algorithm [9] and Niimi’s algorithm [10] so that the original JPEG images can be completely recovered. Joshi’s algorithm uses a prediction-based RDH technique to achieve reversibility and protects sensitive regions by modifying pixel values in them. By embedding the location information into the whole JPEG image with the RDH algorithm in [15], the protected blocks can be identified only after data extraction. The protected blocks are scrambled with a secret key in our proposed algorithm so that it is more difficult for an adversary to recover the original image. Invisibility of the protected content, image quality, reversibility and JPEG file size increment are measured.
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