包装防伪与数字水印

A Publicly Verifiable Copyright-Proving Scheme

Resistant to Malicious Attacks

Tzung-Her Chen,Gwoboa Horng,Member,IEEE,and Wei-Bin Lee,Member,IEEE

Abstract—A wavelet-based copyright-proving scheme that does not require the original image for logo verification is proposed in this paper.The scheme is strong enough to resist malicious ma-nipulations of an image including blurring,JPEG compression, noising,sharpening,scaling,rotation,cropping,scaling-cropping, and print–photocopy–scan attacks.The proposed scheme is also re-sistant to StirMark and unZign attacks and it is not only a robust method but also a lossless one.Experiments are conducted to show the robustness of this method.Moreover,cryptographic tools,such as digital signature and timestamp,are introduced to make copy-right proving publicly verifiable.

Index Terms—Copyright protection,digital signature,digital timestamp,digital watermarking,discrete wavelet transform.

I.I NTRODUCTION

T HERE is no doubt that the progress of networking tech-nology has enabled much faster and easier distribution of digital documents.Moreover,duplicating digital documents has become as simple as clicking a button.Accordingly,the issue of copyright protection has become more imperative than ever. Furthermore,the current problems with copyright protection ob-struct the rapid evolution of computer and communication net-works[1].Hence,the enhancement and further development of digital copyright protection is central to the development of fu-ture communication networks.

The current cryptographic techniques,such as encryption, digital signature,and digital timestamp,[2]while suitable for text documents,are not suitable for protecting multimedia data such as images,audio,and video directly.Firstly,thefile size is much greater than that of text.Hence,more time is needed to encrypt/sign them.Secondly,no distortion is allowed in en-crypted/signed text.However,this requirement is not always necessary for the multimedia data.

Recently,digital watermarking techniques have received considerable attention,since they have high commercial poten-tial for copyright protection and authentication for multimedia data.A digital watermarking technique embeds a watermark, including a signature or a copyright message,such as a trade logo,a seal,or a sequence number,into an image.Subsequently, the watermark can be extracted/detected from the watermarked image and be adopted to verify the ownership.

Manuscript received August22,2002;revised December26,2003.Abstract published on the Internet November10,2004.

T.-H.Chen and G.Horng are with the Institute of Computer Science, National Chung Hsing University,Taichung402,Taiwan,R.O.C.(e-mail: phd9007@.tw;gbhorng@.tw).

W.-B.Lee is with the Department of Information Engineering,Feng Chia University,Taichung407,Taiwan,R.O.C.(e-mail:lwb@.tw). Digital Object Identifier10.1109/TIE.2004.841083

With copyright protection in mind,a watermarking scheme must satisfy six essential properties.First,a watermark must have transparency.That is to say,the embedded watermark must be perceptually invisible.In other words,the embedding process should not distort the image from the human visual aspect.The second is robustness.The embedded watermark must be strong enough to resist against attacks intending to remove the water-mark.These attacks include:image processing(blurring,JPEG compression,noising,and sharpening)and geometric distortions (scaling,rotation,cropping,and print–photocopy–scan).The third property is unambiguity.A watermarking technique must identify the owner of an image without ambiguity.The fourth property is security.According to Kerckhoff’s principle,the security of a cryptosystem should not depend on keeping the cryptographic algorithm secret[2].Security depends only on keeping the key secret.For the same reason,the security of the watermark should not depend upon the assumption that the pirate does not know the watermarking algorithm.The watermarking algorithm must be public while the embedded watermark is undeletable.Thefifth property is blindness.In the watermark verification phase,it is not necessary to use the original image in identifying the embedded watermark.That is,the copyright owners need no extra disk space to preserve the original image. The sixth andfinal essential property it must be able to have is multiple watermarking.In a multiple watermarking scheme, more recent watermarks(for legal distributors and users)must not interfere with the original watermarks.

Copyright protection is limited today because almost all pro-posed watermarking technology cannot simultaneously meet all of these properties.One of the most cited watermarking schemes is proposed by Cox et al.in[3].The authors embed the water-mark sequence into the highest magnitude discrete cosine trans-form coefficients.Since the watermark is cast into the most per-ceptually significant regions of the original image,it is tough enough to resist common signal processing and geometric dis-tortions.In[4]and[5],the authors propose the discrete co-sine/wavelet transform schemes to embed watermarks by mod-ifying the middle-frequency coefficients.Unfortunately,their schemes are sensitive to simple geometric distortions.In[6], cocktail watermarking is proposed by Lu and Liao.They si-multaneously insert two complementary watermarks into the original image incorporating a modulation strategy.One em-bedded watermark is based on a positive modulation rule,used to increasingly modulate the selected wavelet coefficients of the original image and the other a negative modulation rule,used to decreasingly modulate the selected wavelet coefficients of the original image.Thus,no matter what kind of attack is encoun-tered,at least one watermark will survive.Although many at-

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