DigitalWatermark

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DIGITAL WATERMARKING

Ng Huy Phc 50701831

Trn Kim Ln 50701259Phm Quc Hip 50700812


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PART 1

INTRODUCTION


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STEGANOGRAPHY

Steganography(art of hidden writing)

The art and science of writing hiddenmessages in such a way that no one apart

from the intended recipient knows of the

existence of the message.

The existence of information is secret.


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Histaeus used his slaves (information tattooed

on a slavesshaved head)

Initial Applications of information hiding

Passing Secret messages

STEGANOGRAPHY


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STEGANOGRAPHY

Physical steganography


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STEGANOGRAPHY

Digital steganography

Network steganography


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DEFINITION

The process of embedding information into a

digital signal in a way that is difficult to

remove.

The signal may be text, images, audio, video.

The information is also carried in the copy if

the signal is copied.


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DEFINITION

Example:


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GENERAL APPLICATIONS

Copyright Protecton

To prove the ownership of digital media.


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Tamper proofing

To find out if data was tampered.



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Quality Assessment

Degradation of Visual Quality

Loss of Visual Quality



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LIFE-CYCLE PHASES

Attemp to

extract

watermark

from signal

The markedsignal is

modified

Producewatermarked

signal


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CLASSIFICATION

Digital watermarking techniques can be

classified in many ways :

Visibility

Robustness

Perceptibility Capacity

Embedding method


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VISIBILITY

Visible

Text or a logo which identifies the owner of the

media.

Invisible

Information is added as digital data to audio,

picture or video, but it cannot be perceived.

May be a form of Steganography.


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ROBUSTNESS

Robust

Resisted a designated a class of transformations.

Against adversary based attack.

(e.g. noise addition to images)

Used in copy protection application.

Example: Robust Private Spatial Watermarks


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ROBUSTNESS

Fragile

Fail to be detected after the slightest modification.

Used for tamper detection.

Example: Blind Fragile DCT based Watermarks


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PERCEPTIBILITY

Perceptible

Its presence in the marked signal is noticable, but

non-intrusive.

Imperceptible

Original cover signal and the marked signal are

close to perceptually indistinguishable.


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PERCEPTIBILITY

Stanford Bunny 3D Model Visible Watermarks in Bunny

Model Distortion

Watermarking

Stanford Bunny 3D Model

Watermarking

Invisible Watermarks in Bunny Model

Minimal Distortion


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CAPACITY

Depend on the length of the embedded

message.

Zero-bit long

Detect the presence or absence of the watermark.

A 1 denotes the presence. 0 denotes the absence.

N-bit long

Modulated in the watermark.

Support multiple watermarks.


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EMBEDDING METHOD

Spread-spectrum

The marked signal is ontained by an additive

modification.

Modestly robust.

Have a low information capacity.


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EMBEDDING METHOD

Quantization type

The marked signal is ontained by quantization

Low robustness.

Have a high infoirmation capacity.

Amplitude modulation

The marked signal is ontained by additive

modification similar to spread spectrum method.

Embedded in the spatial domain.


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As much information (watermarks) as possible.

Capacity

Only be accessible by authorized parties.

Security Resistance against hostile/user dependent

changes

Robustness

Invisibility

Imperceptibility

DESIGN REQUIREMENTS


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PART 2

SPECIFIC WATERMARKING

TECHNIQUES ON IMAGES


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A very simple yet widely used technique for

watermarking images is to add a pattern on top

of an existing image.

Usually this pattern is an image itself - a logo orsomething similar.

SIMPLE WATERMARKING


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The LSB technique is the simplest technique of

watermark insertion.

Consider a still image : each pixel of the colorimage has three components red, green and

blue.

Allocate 3 bytes for each pixel. Then, each colourhas 1 byte, or 8 bits.

LSB : LEAST SIGNIFICANT BIT


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A pixel that is bright purple in colour can be showN

as X0 = {R=255, G=0, B=255}

Look at another pixel: X1 = {R=255, G=0, B=254}

Detecting a difference of 1 on a color scale of 256

is almost impossible for human eye.

Replace the color intensity information in the

LSB with watermarking information, the image will

still look the same to the naked eye.



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Use a secret key to choose a random set of bits.

The more bits used in the host image, the more it

deteriorates.

Increasing the number of bits used though

obviously has a beneficial reaction on the secret

image increasing its clarity.



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Host image is on the left,

watermark image is on the right



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Watermarking in the frequency domain involves

selecting the pixels to be modified based on the

frequency of occurrence of that particular pixel.

Transform an image into the frequency domain. A block-based DCT watermarking approach is

implemented.

An image is first divided into blocks and DCT isperformed on each block. The watermark is then

embedded by selectively modifying the middle-

frequency DCT coefficients.

FREQUENCY-BASED TECHNIQUES


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What is DCT ?

Formally, the discrete cosine transform (DCT)

is a linear, invertible function

F: RN-> RN(where Rdenotes the set of realnumbers), or equivalently an invertible N Nsquare

matrix



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Discrete wavelet transform (DWT)

The image is separated into different resolution

The original image is high-pass filtered, yielding

the three large images, each describing local

changes details in the original image It is then low-pass filtered and downscaled,

yielding an approximation image.

This image is high-pass filtered to produce thethree smaller detail images.

And low-pass filtered to produce the final

approximation image in the upper-left.

WAVELET WATERMARKING TECHNIQUES


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Embedding the watermark The host image and watermark are transformed

into wavelet domain.

The transformed watermark coefficients wereembedded into those of host image at each

resolution level with a secret key.



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A Narrow-band signal is transmitted over a muchlarger bandwidth such that the signal energy

presented in any signal frequency is undetectable

A watermark is spread over many frequency binsso that the energy in one bin is very small and

certainly undetectable.

SPREAD-SPECTRUM TECHNIQUES


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Because the watermark verification process knowsthe location and content of the watermark, it is

possible to concentrate these weak signals into a

single output with high SNR (Signal-to-noise ratio).

Remark

To destroy such a watermark would require noise of

high amplitude to be added to all frequency bins.

The location of the watermark is not obvious. Frequency regions should be selected that ensures

degradation of the original datafollowing any attack on

the watermark.



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References

Techniques and Applications of Digital

Watermarking and Content ProtectionMichael Arnold, Martin Schmucker, Stephen D. Wolthusen

Steganography And Digital Watermarking

Jonathan Cummins, Patrick Diskin, Samuel Lau and

Robert Parlett,

School of Computer Science, The University of Birmingham.

Real-Time Digital Image Watermarking

Subramaniam Ganesan, Professor of Oakland University,

Michigan


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PART 3

ATTACKING METHODS


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Foundations of Attacking

3 effects make detection of watermarking

useless:

Watermark cannot be detected.

False watermarks are detected.

Unauthorized detection of watermark.


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Classification of Attacking

Removal attacks

Geometrical attacks

Cryptographic attacks

Protocol attacks


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Classification of watermarking attacks


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Removal Attacks

Most obvious method

Aim for complete removal of watermarking

Extreme form of this type is restore the

original object

Can happen unintentionally due to operations

in some certain applications.


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Geometrical Attacks

Do not actually remove the embedded

watermark

Intend to distort the watermark detector

synchronization with the embedded

information


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Cryptographic Attacks

Aim at cracking the security methods in

watermarking schemes

Finding a way to remove the embedded

watermark information

Embed misleading watermarks

High computational complexity


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Protocol Attacks

Aim at attacking the entire concept of the

watermarking application

First proposed in framework of invertible

watermark

The attacker subtracts his own watermark

from the watermarked data and claims to be

the owner

Another type is copy attack


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Some Methods

Collusion Attack

Estimate the watermark from different works with

same watermark

The attackers can obtain an approximation of thewatermark by averaging the watermarked works


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Some Methods

Remodulation Attack

Damage watermark base on watermark estimation


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Some Methods

Copy Attack

Estimate a watermark from watermarked data and

copy it to some other data

Documents

DigitalWatermark