Digital Watermarking

Presentation for W20026455

Anil Kumar M

12 November 2007

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Contents:

1. Abstract2. Introduction3. Watermarking System4. Types of Digital Watermarking5. Image Watermarking6. Applications7. EC Watermarking Software Example 8. Conclusion9. References

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ABSTRACT

With the growing popularity of digital Medias through the World Wide Web,

intellectual property needs copyright protection, prevention of illegal copying and

verification of content integrity. The new data hiding techniques need to be developed

that satisfy the requirements of imperceptibility, robustness, capacity, or data hiding rate

and security of the hidden data etc. At this stage, water marking plays the role of an

efficient tool. The objective of this project is to explore the basic concepts of digital

water marking and various types and techniques involved in the water marking.

1. INTRODUCTION

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1. Protection of Copyrighted Digital Content

Historically, copyright laws have protected authored content by restricting distribution and modification of the content. The effectiveness of these laws, however, depends on three important requirements:

The creator of original content must be able to refute anybody else’s claim to having created that content. Creators and owners must be able to track the distribution of their content, so that they can detect attempts to distribute it illegally. Illegal attempts to alter the content and distribute it as if it were genuine must be detectable.

Today, creators and owners of digital video, audio, and images want assurance that their content will not be illegally redistributed. Unless content owners are confident that their works will be properly compensated and acknowledged, few would willingly make their content publicly available. Also, consumers want assurance that the content they buy is legitimate. Without mechanisms to support the above requirements, copyright owners cannot generate proof that somebody else violated copyright law.

The techniques that have been proposed for solving this problem are collectively called digital watermarking. Digital watermarking refers to the embedding of unobtrusive marks or labels that can be represented as bits in digital content.

2. WATERMARKING SYSTEMS

2.1 Introduction

Powerful signal processing techniques and ease of modification have made the world shift towards digital representation of multimedia signals such as image, audio and video. The rapid growth of Internet is also fuelling this process. The vendors however, fear to put their multimedia data over the Internet, because there is no way to track the illegal distribution and violation of copyright protection. Watermarking comes into the scenario as a powerful solution to this problem. The important feature of watermarking is that the ordinary users may not detect its presence in the product.

2.2 Properties of Watermarks

There are a number of measurable characteristics that a watermark should exhibit. These include that it should be difficult to notice, robust to common distortions of the signal, resistant to malicious attempts to remove the watermark, support a sufficient data rate commensurate with these application, allow multiple watermarks to be added and that the decoder be scalable.

2.2.1 Imperceptibility

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The watermark should not be noticeable to the viewer, nor should then watermark degrade the quality of the original image. However, if a signal is truly imperceptible, then perceptually based lossy compression algorithms probably, still leave room for an imperceptible signal to be inserted.

2.2.2 Robustness

The watermark must be difficult to remove. If only partial knowledge is available (e.g. the exact location of the watermark in an image is unknown) then attempts to remove or destroy a watermark, should result in severe degradation in fidelity before the watermark is lost.

2.2.3 Common signal processing

The watermark should still be retrievable even if common signal processing operations are applied to the data. These include digital to analog and analog to digital conversion, re-sampling and re-quantization and common signal enhancements to image contrast and color, or audio bass and treble.

2.2.4 Common Geometric Distortions (Image & Video data)

Watermarks in image and video data should also be immune from geometric image operations such as rotation, translation, cropping and scaling.

2.2.5 Universal

The same digital watermarking algorithm should apply to all the three media under considerations. This is potentially helpful in the watermarking of multimedia products. Also, this feature is conductive to the implementation of audio and image/video watermarking algorithms on common hardware.

2.2.6 Unambiguous

The watermark retrieval should unambiguously identify the owner. Furthermore, the accuracy of owner identification should degrade gracefully in the face of attack. In addition, the watermark procedure also ensures low false positive and low false negative detections.

2.3 GENERAL FRAMEWORK FOR WATERMARKIN

In general, any watermarking scheme (algorithm) consists of three parts.

The watermark.

The encoder

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The decoder.

Each owner has a unique watermark or an owner can also put different

watermarks in different objects the marking algorithm incorporates the watermark

into the object. The verification algorithm authenticates the object determining both

the owner and the integrity of the object.

2.3.1 ENCODING PROCESS

Let us denote an image by a signature by S=s1,s2 and the watermarked image

by I. E is an encoder function, it takes an image I and a signature S, and it generates a

new image which is called watermarked image , mathematically,

E(S, I) =Ỉ. (1)

Following figure illustrates the encoding process.

Fig 1.Encoding Process.

2.3.2 DECODING PROCESSA decoder function D takes an image J (J can be a watermarked or un-

watermarked image, and possibly corrupted) whose ownership is to be determined

and recovers a signature Ś from the image. In this process an additional image I can

also be included which is often the original and un-watermarked version of J. This is

due to the fact that some encoding schemes may make use of the original images in

the watermarking process to provide extra robustness against intentional and

unintentional corruption of pixels. Mathematically

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D (J, Ỉ) = Ś. (2)

Following figure illustrates the Decoding process

Fig 2.Decoding process.

3. TYPES OF DIGITAL WATERMARKSWatermarks and watermarking techniques can be divided into various

categories in various ways. The watermarks can be applied in spatial domain. An

alternative to spatial domain watermarking is frequency domain watermarking. It has

been pointed out that the frequency domain methods are more robust than the spatial

domain techniques. Different types of watermarks are shown in the figure below

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Fig 3.Types of Watermarking.

Watermarking techniques can be divided into four categories according to the type of

document to be watermarked as follows.

Image Watermarking

Video Watermarking

Audio Watermarking

Text Watermarking

According to the human perception, the digital watermarks can be divide into three

different types as follows.

Visible watermark

Invisible-Robust watermark

Invisible-Fragile watermark

Dual watermark

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4. IMAGE WATERMARKING

There are plenty of image watermarking techniques algorithms available. In

this section we will discuss a one technique Discrete-Cosine-Transform (DCT).

In DCT technique divide the host image into different blocks, find the DCT of each

block. Then they classify the blocks into six different classes in the increasing order

of noise sensitivity, such as edge block, uniform with moderate intensity, uniform

with high or low intensity, moderate busy, busy and very busy. Each block is then

assigned.

Fig 4.Visible watermarking algorithm

Different α and β values. The host image blocks are then modified as follow:

x¬ = αxij+ β wij (4).

Where xij is the i,j DCT co-efficient of the watermarked image, xij is the

corresponding DCT co-efficient of the original image and wij is the DCT co-

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efficient of the watermark image. Fig. 4 gives the schematic representation of

the technique and Fig. 5 show various results.

Fig. 5 various results.

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5. APPLICATIONS

Digital Watermarks are potentially useful in many applications, including:

5.1 Ownership assertion:

Watermarks can be used for ownership assertion. To assert

ownership of an image, Alice can generate a watermarking signal using a secret private

key, and then embed it into the original image. She can then make the watermarked

image publicly available. Later, when Bob contends the ownership of an image derived

from this public image, Alice can produce the unmarked original image and also

demonstrate the presence of her watermark in Bob’s image. Since Alice’s original image

is unavailable to Bob, he cannot do the same. For such a scheme to work, the watermark

has to survive image processing operations aimed at malicious removal. In addition, the

watermark should be inserted in such a manner that it cannot be forged as Alice would

not want to be held accountable for an image that she does not own.

5.2. Copy prevention or control:

Watermarks can also be used for copy prevention and control. For

example, in a closed system where the multimedia content needs special hardware for

copying and/or viewing, a digital watermark can be inserted indicating the number of

copies that are permitted. Every time a copy is made the watermark can be modified by

the hardware and after a point the hardware would not create further copies of the data.

An example of such a system is the Digital Versatile Disc (DVD). In fact, a copy

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protection mechanism that includes digital watermarking at its core is currently being

considered for standardization and second generation DVD players may well include the

ability to read watermarks and act based on their presence or absence.

5.3 ID card security:

Information in a passport or ID (e.g., passport number, person’s

name, etc.) can also be included in the person’s photo that appears on the ID. By

extracting the embedded information and comparing it to the written text, the ID card can

be verified. The inclusion of the watermark provides an additional level of security in

this application. For example, if the ID card is stolen and the picture is replaced by a

forged copy, the failure in extracting the watermark will invalidate the ID card.

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6. EC Watermarking Software Example:

6.1 Import Image File

6.2 Watermark Setting Screen

6.3 Export Image Screen

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CONCLUSIONDigital watermarking holds significant promise as one of the keys to protecting

proprietary digital content in the coming years. It focuses on embedding information

inside a digital object such that the embedded information is in separable bound to the

object. Tampering with the watermark or otherwise altering a watermarked object

should always be detectable, and attempting to remove a watermark from its object

should cause to be that object useless. Currently, watermarking suffers from several

drawbacks that prevent it from providing the creators of digital content with a solid

guarantee of copyright protection.

The watermarking research is progressing very fast and numerous researchers

from various fields are focusing to develop some workable scheme. Different companies

also working to get commercial products. We hope some commercial and effective

schemes will be available in future.

References:

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Digital Watermarking, by Minerva Yeung, Communications of the ACM.

Technical Trials and Legal Tribulations, by Craver, Yeo, and Yeung, Communications of the ACM, A Survey of Digital Watermarking, by Elizabeth Ferrill and Matthew Moyer, http://www.cc.gatech.edu/~mjm/dw/watermarking.htmlDigital Watermarking, by James Greenfield, http://www.cs.uct.ac.za/courses/CS400W/NIS/papers99/jgreenfi/

Commercial Watermarking Systems:

http://www.ecwatermark.com/download.asphttp://www.digimarc.com/imaging/ibplus_over.htmhttp://www.signumtech.com/docs/suresign/technology.htmlshttp://www.signumtech.com/docs/veridata/technology.htmlhttp://www.bluespike.com/giovanni.htmlhttp://www.mediasec.com/products/syscop.html

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