Dig watermarking

7/28/2019 Dig watermarking

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Digital Watermarking

NIKHIL BADOLA

B.TECH (SE)

Roll No- DSE/2K9/035


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Introduction

Nowadays, in every field there is enormous use of digital

contents. Information handled on internet and multimedia network system

is in digital form.

Advantages Of Digital Document

Efficient data storage and

transmission

Easy manipulation

Copying Without Quality Loss

Disadvantages of Digital Documents

Duplication

No Copyright Protection

No Owner Identification

Todays world is digital world


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Need of Digital Watermarking

The disadvantages of storing information in digital form has led

to the need of digital watermarking because:-

Copies can be produced easily and

inexpensively which are indistinguishable from the original.

Copies can be distributed rapidly.

For proof of Ownership.


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What is Watermarking?

WatermarkRecognizable image or pattern in paper that appears lighterwhen

viewed by transmitted light.

common examples:-

Currency Notes, Stamps,

Passports, Legal Documents

Digital Watermark

A digital watermark is a digital signal or pattern inserted intoa digital document such as text, graphics or multimedia,and carries information unique to the copyright owner, thecreator of the document or the authorized consumer.

If the signal is copied, then the information also iscarried in the copy.


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Watermarking History

Watermarks were used to keep track of paper provenance andquality identification in the art of handmade papermaking nearly

700 years ago.

1993-1994

First papers on digital watermarking 1995

First special session on image watermarking at NSIP95,Neos Marmaras , Greece.

1995

One of the first image watermarking algorithms Patchworkalgorithm


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Properties of Watermarks

Robustness- The robustness describes whether watermarkcan be reliably detected after performing some mediaoperations.

Perceptual transparency-This property describes thatwhether watermark is visible or invisible.

Security- Security property describes that how easy toremove a watermark.

Complexity- Complexity is concerned with amount of effort

needed to extract or retrieve the watermark from content. Capacity-It refers to amount of information that can be

embedded within the content . More is the data used inwatermark ,watermark will become less robust.


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Classification of

Watermarks Perceptible and imperceptible- Perceptible watermarks are

visible to human eye while imperceptible watermarks areinvisible.

Robust & Fragile- Robust or fragile is nothing but degree towhich watermarks can withstand any modifications. Robustwatermarks are those watermarks which are difficult toremove from the object in which they are embedded.

Public & Private- Private watermarks requires atleastoriginal data to recover watermark information. Publicwatermarks requires neither original data nor embedded

watermarks to recover watermark information. Symmetric & Asymmetric- In symmetric the key for

embedding and detection of the watermark are identicalwhereas in asymmetric, the watermark is embedded into theoriginal data with aid of a private and a public key.


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Examples Of Watermarks

visible watermark Invisible Watermark


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Working of Digital WatermarkingThree processes :-

Watermark insertion

Watermark extraction

Watermark Detection

Inputs to insertion unit are

original image (i.e any digital content)

the watermark

user key to obtain watermarked image

1)Insertion

unit


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The input to extraction unit consists of

watermarked image and

key used during insertion unit

Used to see if any digital content containing watermark has

been tampered or not.

Used for allowing any procedure to take place depending on

whether the correct watermark is present or not.

2)Extraction

unit

3)Detection

unit


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Digital Watermarking

techniques Text-based Watermarking

Image Watermarking

Audio Watermarking Video Watermarking


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Watermarking Techniques for

Texts Line-shift Coding:Change the spacing between lines.

Word-shift Coding:Change the spacing between words.

Character Encoding:Change the shapes of characters.

Word-shift coding example:-


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Character encoding example

But these are easily defeated

Retyping the text destroys the watermark

Word processors change the spacing between

words and linesCharacter encoding can be defeated by

changing the font


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Watermarking Techniques for

Images

1) Spatial DomainWatermarking Direct usageof data to embed and extract

Watermark by modifying pixelvalues(for image)

Spread spectrum approach

Least significant bitsubstitution

2) Transform DomainWatermarking Conversion ofdata to another format to

embed and extract.

DCT(discrete cosinetransformation)


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Spread Spectrum

Watermarking used to spread the watermark all over the host image.

The watermark is transformed into a bit string b1,b2.

For each bit bi , a pseudorandom matrix Ri of integers {1-1} isgenerated.

Rimatrices depend on the bi of the watermark

A matrix +Riis used ifbirepresents a 0,

A matrix-Riis used ifbi represents a 1

sum of all random patterns Ri defines the watermark W:

W = Ri

watermarked image IWis generated by adding the watermark intocover imageI IW = I + W


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LSB substitution

LSB substitution simply converts the least significant bit(s) of

cover image to watermark.

Since only the LSBs are changed, the modification does not

cause much perceptible noise to the cover.


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Robustness of LSB methodLSB substitution is not robust against attempts to remove the

watermark.

A simple modification of the image (e.g., by setting all LSBs

of all pixels to 0) can wipe out the watermark.

Transcoding (such as converting the image into lossy

JPEG file) can also remove the watermark effectively.


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A DCT-based techniqueDCT separates the image into parts of differing importance(wrt image quality)

Given a cover image, we first decompose it into a number of

88 blocks of pixels. These squares is transformed via a DCT, which outputs a 2D

array of 64 coefficients

If the watermark contains n bits, use a secret key to locate nblocks at pseudo-random locations.

These blocks Bi is used to carry the n bits of the watermark.


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Attacks on Watermarks

Mosaic attackThis is done by dividing the original image into randomly sizedsmall images and displaying the resulting image on webpage

so as to confuse watermark-searching program known as Web-Crawler.

Geometric attackGeometric attack is related to geometric properties of data andis further classified as-

Subtractive attack=> It involves the attack in the area oflocated watermark if imperceptible and then removing the markby cropping or editing.

Distortive attack=> In this attack, attacker attempts tomake some uniform distortive changes in the images such thatmark becomes unrecognizable.


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Stirmark attack

stirmark involves resampling process in which it introducessome kind of errors into an image to print it on high qualityprinter and scanning it again with high quality scanner. It

includes minor geometric distortion. Forgery attack

Forgery attack include the attacker who can add his or herown watermark overlaying the original image and marking the

content as their own.

Cryptanalysis

It is a method in which attacker attempts to find the decryptionkey and remove licensing watermark.


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Watermark Application Authentication

The creator of a content can embed a fragile watermarkinto the content to provide a proof of authenticity. Anytampering of the original content destroys the watermark andthus can be detected.

Broadcast monitoringBroadcast content is embedded with a unique identifier

making content and corresponding broadcasters instantlyidentifiable. Using specialized software able to retrieve, andanalyze the data, reports are sent to the owner.

Copy PreventionCopy prevention helps the digital watermarks to identify

whether the content can be copied. It guards againstunauthorized duplication.

Fingerprinting

Hidden serial numbers. It enable the intellectual propertyowner to identify which customer broke his license agreement.


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Limitations of Watermarks

Cannot be inserted if it downgrades the quality of the sourceimage too much.

Digital watermark readers are usually widely available.

There is a limited amount of data that can be used to insert

digital watermarks in a highly compressed JPEG image. Certain media operations like image compression usually

destroy watermarks easily.


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Conclusion

The large need of networked multimedia system has createdthe need of COPYRIGHT PROTECTION.

It is very important to protect intellectual properties of digitalmedia.

Internet playing an important role of digital data transfer.Digital watermarking is the great solution of the problem ofhow to protect copyright.

Digital watermarking is the solution for the protection of legalrights and interests of digital content owner and customer.

Existing schemes provide only limited measures of marking.


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References

http://en.wikipedia.org/wiki/Digital_wat

ermark

http://www.google.com http://www.yahoo.com


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Thank you

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