Steganalysis of a PVD-based content adaptive image steganography
Highlights
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PVD is a well-known technique for content adaptive steganography.
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A targeted detector is devised to detect a recently proposed PVD-based method.
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The PVD-based method can be detected even at a low ER of 0.05 bpp.
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A theoretical analysis of the proposed method is provided.
Introduction
Steganalysis algorithms can be generally classified into two categories: targeted and universal [1], [2], [3], [4]. Targeted algorithms aim to identify the existence of hidden data embedded by a specific steganographic method, whereas universal algorithms intend to detect a wide range of steganography. We consider digital image as cover data and study the technique of targeted steganalysis in this work.
It is widely accepted that taking the characteristics of natural image into account may enhance stego-security. For example, it is obvious that embedding modifications operated in rough regions of a natural image are less perceptible than that in flat regions. Besides, the slight modifications to rough regions cannot be easily perceived by analyzing usual image statistics since the embedding noise is covered by the inherent noise. Thus the content adaptive approach for steganography has the potential to provide a higher level of security. Based on this consideration, Wu et al. proposed the so-called pixel-value-differencing (PVD) steganography [5], in which the difference value of a pixel pair is considered as a smoothness measurement and more data bits will be embedded into the pair if its difference is relatively large. Thereafter, numerous PVD-based methods are proposed [6], [7], [8], [9] and their security are also discussed [10], [11], [12], [13].
Recently, a new PVD-based method is proposed by Luo et al. [14]. By incorporating PVD with the pairwise embedding algorithm of Mielikainen [15], this method can realize content adaptive embedding and meanwhile provide a better PSNR compared with some previously proposed PVD-based methods. The experimental results reported in [14] show that this method is secure in resisting state-of-the-art steganalyzers.
In this work, we propose a targeted detector to detect Luo et al.'s PVD-based method. We show that although content adaptive embedding is a way to enhance stego-security, Luo et al.'s PVD-based scheme is not a good choice for realizing adaptive embedding since it contains a serious design flaw in data embedding procedure and this flaw can lead to possible attacks. More specifically, by counting the differences of adjacent pixels in both vertical and horizontal directions, a folded difference-histogram is generated and we show that Luo et al.'s PVD-based method may arise significant artifact to this histogram which can be exploited for reliable detection. By our detector, Luo et al.'s PVD-based method can be detected even at a low embedding rate (secret data bits embedded per pixel, ER for short) of 0.05 bits per pixel (bpp).
The rest of this paper is organized as follows. First, the embedding procedure of Luo et al.'s method is described in Section 2. Then, to better present our idea, we consider to detect a simple case of Luo et al.'s method in Section 3.1. A theoretical analysis of our method for this simple case is also provided. Next, the proposed detector for the general case of Luo et al.'s method is introduced in Section 3.2. Finally, experimental results are reported and conclusions are drawn in 4 Experimental results, 5 Conclusion, respectively.
Section snippets
Embedding procedure of Luo et al.'s method
The data embedding procedure of Luo et al.'s method is described step by step as follows. Some remarks are also included in the description.
Step 1 (pixel pair partition): First, for a pre-selected integer , divide the cover image into non-overlapped blocks of pixels. Then, for each pixel block, rotate it by a pseudo-random degree chosen from {0°,90°,180°,270°}. Next, rearrange the resulting image as a row vector V by raster scanning. Finally, divide V into non-overlapped
A case study with the block size Bz=1
We consider in this subsection a simple case of Luo et al.'s method where the block size Bz is fixed at 1. Such a case equivalently skips the processing before image raster scanning in Step 1 of Section 2.
Define the difference-histogram of cover image aswhere V is the set defined in Step 1 of Section 2. The corresponding difference-histogram of stego image noted as hs can be defined in a similar way. From Table 1, the change of difference-histogram due to data
Experimental results
The experiments are performed on the BOSSBase v1.00 database [19] which contains 10,000 512×512 gray-scale images. The stego images are obtained by Luo et al.'s method with random and different ER. Then the detector D defined in (22) is computed for both cover and stego images.
The proposed detector is evaluated by comparing it with following prior arts: the second order SPAM proposed by Pevny et al. [20], and the recently proposed detector [12] of Tan and Li which is specifically
Conclusion
In this work, we devised a targeted detector for detecting the recently proposed PVD-based embedding method [14]. We have shown that this PVD-based method may arise significant artifact to the difference-histogram, and it can be well detected even for an ER as low as 0.05 bpp. In this light, we conclude that the PVD-based method [14] is not a good choice to realize content adaptive embedding.
Acknowledgments
The authors would like to thank Dr. Shunquan Tan of Shenzhen University, Shenzhen, China, for providing us the source code in [12]. The work of Bin Li was supported by National Natural Science Foundation of China (61103174) and Fundamental Research General Program of Shenzhen City (JCYJ20120613113535357). The work of Xiangyang Luo was supported by Postdoctoral Science Foundation of China (2012T50842).
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