Optical Watermarking

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WELCOME

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DIGITAL WATERMARKING

FOR DOCUMENTS

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CONTENTS

IntroductionLiterature ReviewProposed WorkConclusionReferences

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INTRODUCTION

Watermark :- Recognizable image or pattern in paper.

Digital watermark :- Encoding an identifying code into digitized music, video, picture, or other file.

Watermarking :- Techniques that allow secret communication , usually by embedding or hiding the secret information

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LITERATURE REVIEW

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HISTORY OF WATERMARKS

The first watermark was invented in 1826 by John Marshall. A watermark is made by impressing a water-coated metal stamp or dandy roll onto the paper during manufacturing.

Another type of watermark is called the cylinder mould watermark. A shaded watermark, first used in 1848, incorporates tonal depth and creates a greyscale image.

The first stamp on watermarked paper was issued in April of 1895.

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HISTORY OF DIGITAL WATERMARKING

The term "digital watermark" was first coined in 1992 by Andrew Tirkel and Charles Osborne in their paper A.Z.Tirkel, G.A. Rankin, R.M. Van Schyndel, W.J.Ho, N.R.A.Mee, C.F.Osborne. “Electronic Water Mark”. DICTA 93, Macquarie University. p.666-673.

The term used by Tirkel and Osborne was originally used in Japan-- from the Japanese-- "denshi sukashi" -- literally, an "electronic watermark".

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BASIC WATERMARKING PRINCIPLES

The public or secret key is used to enforce security Many watermarking schemes use spread-spectrum

methods , they add a PN signal with low amplitude to the host data.

Correlator is used for watermark detection.

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WATERMARKING REQUIREMENTS

Capacity :- As much information as possible.

Security :- Only be accessible by authorized parties by means of cryptographic key.

Robusteness :- Resist against hostile.

Invisibility.

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CLASSIFICATION OF DIGITAL WATERMARKING

Digital watermarking techniques may be classified in several ways.

Robustness :-A digital watermark is called robust if it resists a designated class of transformations.

Perceptibility :-A digital watermark is called perceptible if its presence in the marked signal is noticeable.

Capacity :-The length of the embedded message .

Embedding method :- Spread spectrum , quantization and modulation.

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TYPES OF WATERMARKING TECHNIQUES

Fig 3. Watermarking Techniques

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DIGITAL WATERMARKING SYSTEM

Fig 4. Digital Watermarking system

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PURPOSE OF DIGITAL WATERMARKING

Ownership Assertion – to establish ownership of the content (i.e. image)

Fingerprinting – to avoid unauthorized duplication and distribution of publicly available multimedia content

Authentication and integrity verification – the authenticator is inseparably bound to the content whereby the author has a unique key associated with the content and can verify integrity of that content by extracting the watermark.

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CONT’D….

Usage control – added to limit the number of copies created whereas the watermarks are modified by the hardware and at some point would not create any more copies (i.e. DVD)

Content protection – content stamped with a visible watermark that is very difficult to remove so that it can be publicly and freely distributed

Content labeling – bits embedded into the data that gives further information about the content such as a graphic image with time and place information.

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ATTACKS ON WATERMARK

Active Attacks – hacker tries to remove the watermark or make it undetectable. An example is to crop it out.

Passive Attacks – hacker tries to determine whether there is a watermark and identify it. However, no damage or removal is done.

Collusion Attacks – hacker uses several copies of one piece of media, each with a different watermark, to construct a copy with no watermark.

Forgery Attacks – hacker tries to embed a valid watermark of their own rather than remove one.

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APPLICATIONS Copyright Protection

Invisibly mark products. Authentication (temper detection, monitoring). Manage distribution of assets

Apply unique watermark key to each copy of a distributed video/image.

Embed all necessary data in a single image. Many more, including

-(Multi-level) secure data systems in military,-medical and law enforcement fields.-Digital notarization..-On-line identity verification.

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PROPOSED WORK In this paper, we present a novel and simple

optical watermarking system aiming at overriding some practical problems when digital watermarking techniques are applied to authenticate the printed documents.

Optical watermarking differing from traditional digital watermarking in a sense that the watermark extraction is done by some optical and visual means like photocopier. While no any digitization is required.

The system security is guaranteed by adopting content-based key share scheme originated from visual cryptography.

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SYSTEM OVERVIEW AND SECURITY

Our proposed solution mainly originates from two different research fields: -

Visual cryptography Frequency modulation.

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VISUAL CRYPTOGRAPHY

The idea of visual cryptography was independently invented by G.R. Blakley and A. Schamir which originated from traditional topic in cryptography: secret sharing.

In general, a n-out-of-m threshold scheme is a method of sharing a secret K among a set of m participants a way in such that - Any n participants can compute the value of K, and - No group of n-1 (or fewer) participants can compute information about the value of K.

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CONT’D….

Fig 5. A 2-out-of-2 visual threshold scheme

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FREQUENCY MODULATION

For images with a limited bandwidth, it is possible to completely reconstruct the original image if the sampling frequency Ws> 2Wm, where Wm is the highest frequency present in the image.

Fig 6. Watermark embedding and extracting (a) embedding (b) extracting

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WATERMARK EMBEDDING

Two main kinds of modulation methods are employed here :-

Line modulation Dot modulation.

The strength of modulation is actually controlling the line width or doc size. If the value of watermark seed is 1 (black), after zooming in, the corresponding block pixel values should be all 1s. Thus we can modify these 1s by replacing some of them with 0s to form a thin directional line or to form a large dot.

If the value of watermark seed is 0 (white), we can modify all those 0s by replacing some of them with 1 to form a thin line with another direction or to form a small dot. By carefully selecting the zoom in resolution and the direction of the line or the size of the dot, a good visual quality can be still kept after watermark embedding.

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SYSTEM DESCRIPTION

Fig 7. System Diagram

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KEY FORMATION

Fig 8. Key formation

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Fig 9.Watermark image

Fig 11.Extracted Watermark image

Fig 10. Final watermark image

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CONCLUSIONAn optical watermarking solution for document authentication has been given .

We introduced a concept of optical watermarking by conducting document authenticity verification with human eyes.

The system security is guaranteed by adopting visual cryptography in key set generation.

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REFERENCES A.Z.Tirkel, G.A. Rankin, R.M. Van Schyndel, W.J.Ho, N.R.A.Mee,

C.F.Osborne. “Electronic Water Mark”. DICTA 93, Macquarie University. p.666-673.

Meggs, Philip B. (1998). A History of Graphic Design (Third ed.). John Wiley & Sons, Inc.. pp. 58. ISBN 978-0-471-29198-5.

Biermann, Christopher J. (1996). "7". Handbook of Pulping and Papermaking (2 ed.). San Diego, California, USA: Academic Press. p. 171. ISBN 0-12-097362-6.

M. Yeung and F. Mintzer, An invisible watermarking techniques for image verification,IEEE ICIP’97,Santa Barbara, USA, Oct., 1997.

Doug Stinson, Visual cryptography and thresholdscheme,IEEE Potential, pp.13-19, Feb./Mar., 1998.

Q.B. Sun, P.R. Feng and R. Deng, An Optical Watermarking Solution for AuthenticatingPrinted Documents, verification,IEEE ITCC’2001.

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THANKS