08-02-2013, 10:13 AM
Data Hiding in JPEG Images
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INTRODUCTION
Steganography has been an important subject since people
started communicating in writing. Steganography means
hiding a secret message (the embedded message)
within a larger one (source cover) in such a way that an
observer cannot detect the presence of contents of the
hidden message. Today the growth in the information
technology, especially in computer networks such as
Internet, Mobile communication, and Digital Multimedia
applications such as Digital camera, handset video etc. has
opened new opportunities in scientific and commercial
applications. But this progress has also led to many serious
problems such as hacking, duplications and malevolent
usage of digital information. Steganography finds its role in
attempt to address these growing concerns. We know that,
with the use of steganographic techniques, it is possible to
hide information within digital audio, images and video files
which is perceptually and statistically undetectable.
Jpeg-Jsteg
One of the well known embedding method of steganography
based on Transform domain is Jpeg-Jsteg which embeds secret
message (that is, in encoded form with help of Huffman codes)
into LSB of the quantized DCT coefficients. There is one
disadvantage of Jpeg-Jsteg that only few messages can be
embedded in the cover-image. Also, Andreas Westfeld and
Andreas Pfitzmann [11] noticed that steganographic systems
that change LSBs sequentially cause distortionsdetectable by
steganalysis methods. They observed that for a given image, the
embedding of high-entropy data (often due to encryption)
changed the histogram of color frequencies in a predictable
way. J.Fridrich [3] has claimed that her method can potentially
detect messages as short as any single bit change in a JPEG
image.
RESULTS AND ANALYSIS
The proposed algorithm has been implemented on number of
images. The measures such as message capacity (Codeword
length) and PSNR values for the two gray-level cover images
of size 128 x 128, namely, 8.tif (figure 3.1) and 0.tif (figure
3.2) and four 256 x 256 pixels, namely, Lena, Baboon, Peppers
and tree (figures 3.3 to 3.6) obtained from the proposed
algorithm are compared with the corresponding Jpeg-Jsteg
method.
The figures 3.7 and 3.8 are stego-images obtained by Jpeg-
Jsteg using Huffman and proposed T-codes used Jpeg-Jsteg
method.
The results of PSNR values obtained from the existing Jpeg-
Jsteg and proposed methos are summarized in two tables:
Table 3.1 and table 3.2.
CONCLUSION
We observe from our experimental results that PSNR values of
the proposed Jpeg-Jsteg algorithm based on T-codes for the
different images are almost same as that of original algorithm
based on Huffman codes, i.e., there is no change in the stego-
image quality. Our method is secure in the way that even if the
attacker detects (i.e., statistical attacks) and extracts the
embedded message from the stego-image, he/she would not be
able to recover the secret message without the encoded key.
Moreover due to the inherent property of self-synchronizing of
T-codes, our method is more robust as after the extraction
process the recovered secret message is decoded and found to
be without being much destroyed (for results one may refer to
[12])