Cryptography Reference
In-Depth Information
11.2 A Multipurpose Image Watermarking Algorithm
Based on Multistage VQ for Copyright Protection
and Content Authentication
Most of the existing watermarking schemes are designed for copyright pro-
tection or content authentication. In order to fulfill the multipurpose appli-
cations, several multipurpose watermarking algorithms based on wavelet
transform [11] and fast Fourier transform [12] are given. Compared to tradi-
tional watermarking algorithms, there are following extra technical challenges
in designing the multipurpose watermarking schemes. Firstly, the embedding
order of the multiple watermarks should be analyzed in detail. Secondly, how
to reduce the effect of the later embedded watermarks on the former embedded
watermarks is a hard problem to solve. Thirdly, the detection or extraction
of each watermark should be independent. In [11], watermarks are embedded
once in the hiding process and can be blindly extracted for different applica-
tions in the detection process. This scheme has three special features:
1) The approximation information of a host image is kept in the hiding process
by utilizing masking thresholds.
2) Oblivious and robust watermarking is done for copyright protection.
3) Fragile watermarking is done for detection of malicious modifications and
tolerance of incidental manipulations.
In addition to images, both gray-scale and color, this method has been ex-
tended to audio watermarking [12]. It is noted that, unlike multipurpose wa-
termarking, multiple or cocktail watermarking methods [13, 14] are mainly
applied to copyright protection. This is done by embedding multiple robust
watermarks, each one being robust to particular kinds of attacks.
Traditional digital watermarking schemes are mainly based on DCT and
DWT transforms. Recently, some robust image watermarking techniques
based on vector quantization (VQ) [15, 16, 17, 18, 19, 20, 21] have been pre-
sented. References [15, 16, 17, 18] embed the watermark information into the
encoded indices under the constraint that the extra distortion is less than a
given threshold. Reference [19] embeds the watermark bit in the dimension in-
formation of the variable dimension reconstruction blocks of the input image.
References [20, 21] embed the watermark information by utilizing properties,
such as mean and variance, of neighboring indices. In this section, we give a
novel multipurpose watermarking method based on multistage vector quan-
tization. In the proposed algorithm, the robust watermark is embedded in
the first stage by using the embedding method presented in [20]. The semi-
fragile watermark is embedded in the second stage by using a novel index
constrained method. The remainder of this section is organized as follows. In
Section 11.2.1, previous VQ-based watermarking algorithms are reviewed. In
Section 11.2.2, the proposed multipurpose watermarking method is described
in detail. The simulation results are given in Section 11.2.3. The conclusions
are given in Section 11.2.4, respectively.
