dig watermarking
TRANSCRIPT
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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
QUESTIONS????