Jpeg-Jsteg

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  • Topic: JPEG, Data compression, Discrete cosine transform
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INFORMATICA, 2004, Vol. 15, No. 1, 127–142  2004 Institute of Mathematics and Informatics, Vilnius

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High Capacity Data Hiding in JPEG-Compressed Images
Hsien-Wen TSENG, Chin-Chen CHANG
Department of Computer Science and Information Engineering National Chung Cheng University Chaiyi, Taiwan 621, R.O.C. e-mail: {hwtseng,ccc}@cs.ccu.edu.tw Received: March 2003 Abstract. The JPEG image is the most popular file format in relation to digital images. However, up to the present time, there seems to have been very few data hiding techniques taking the JPEG image into account. In this paper, we shall propose a novel high capacity data hiding method based on JPEG. The proposed method employs a capacity table to estimate the number of bits that can be hidden in each DCT component so that significant distortions in the stego-image can be avoided. The capacity table is derived from the JPEG default quantization table and the Human Visual System (HVS). Then, the adaptive least-significant bit (LSB) substitution technique is employed to process each quantized DCT coefficient. The proposed data hiding method enables us to control the level of embedding capacity by using a capacity factor. According to our experimental results, our new scheme can achieve an impressively high embedding capacity of around 20% of the compressed image size with little noticeable degradation of image quality. Key words: JPEG, data hiding, steganography, HVS, Jpeg–Jsteg, LSB substitution.

1. Introduction Image, audio, video, and many other kinds of data are nowadays mostly passed from person to person or from place to place in a digital form. It is often desirable to embed data into the digital contents for copyright control and authentication, or for secret data hiding. Data-embedding techniques designed to take care of such tasks are commonly classified as watermarking or data hiding techniques in accordance with their functionalities. Watermarking techniques are often further divided into two groups: robust watermarking methods and fragile watermarking methods. In robust watermarking methods, the hidden information remains robust against manipulations from any possible sources including hostile ones. Hence such methods are usually developed to protect copyright. On the other hand, fragile watermarking methods are usually designed to easily get broken so that common content processing operations, if there are any at all, can be found. Therefore, such methods are good for tampering detection and authentication. As for those classified as data hiding techniques, they are sometimes called steganographical methods, where the secret message blends in a common digital content, so that eavesdroppers will not have any idea that the secret message is there, and so they will not have the slightest

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intention of trying to break the protection. Under such circumstances, robustness seems to be less stringent, and the major issues here are the embedding capacity and invisibility. In other words, a good data hiding method should be one that can embed as much data as possible, and the perceptual distortion of the digital content after the embedding procedure should be as little as possible. Current methods for the embedding of data into the cover image fall into two categories: spatial-based schemes (Adelson, 1990; van Schyndel et al., 1994; Wang et al., 2001) and transform-based schemes (Cox et al., 1997; Wolfgang et al., 1999; Xia et al., 1997). Spatial-based schemes embed the data into the pixels of the cover image directly, while transform-based schemes embed the data into the cover image by modifying the coefficients in a transform domain, such as the Discrete-Cosine Transform (DCT). In this paper, we will focus upon data hiding in the DCT domain as well as quantized DCT coefficients. We shall embed the data into a JPEG (Pennebaker and Mitchell, 1993) compressed image, for most digital images are stored and transmitted in the...
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