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DigitalDigital WatermarkingWatermarking

Alexander Hasslacher, 0056448Alexander Hasslacher, 0056448

EMTEMT--InstitutInstitut,, JKUJKU--LinzLinz, 2004, 2004

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WhatWhat

isis

aa

WatermarkWatermark

EncoderOriginal Image (I)

Signatur (S)

Watermarked Image (I)

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TypesTypes of Digitalof Digital WatermarksWatermarks

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VisibleVisible

andand

invisibleinvisible

WatermarkWatermark

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LSBLSB

forfor

*.BMP*.BMP

LSBLSB

00100111 11101001 1100100000100111 11101001 11001000

00100111 11001000 1110100100100111 11001000 11101001

11001000 00100111 1110100111001000 00100111 11101001

Hide a binary value for A 10000011Hide a binary value for A 10000011 00100111 111010000100111 111010000 1100100011001000 0010011001001100 11001000 111010011001000 111010000

11001000 00100111 1110100111001000 00100111 11101001

fragile against noise & compressionfragile against noise & compression

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FFT, DCTFFT, DCT

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DCT Domain WatermarkingDCT Domain Watermarking

Watermark embeddingWatermark embedding W: watermark to be embedded.W: watermark to be embedded. X: sequence of pixel valuesX: sequence of pixel values

XXdd and Yand Ydd: row: row--concatenated DCT coefficients of X and Yconcatenated DCT coefficients of X and Y A=scaling factor: Determines the intensity of the watermarkA=scaling factor: Determines the intensity of the watermark

YYdd(i(i) = X) = Xdd(i)(1+aW)(i)(1+aW)

Watermark extractionWatermark extraction W*: extracted version of the watermarkW*: extracted version of the watermark ZZdd: possibly forged watermarked image.: possibly forged watermarked image.

T=userT=user--defined thresholddefined threshold If S > T, image is authenticIf S > T, image is authentic

*

***

*

*),(1

)(

)(1)(

WW

WWWWS

iX

iZ

a

iW

d

d===>=

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ConclusionsConclusions Modification ofModification ofallall DCT coefficients distorts the imageDCT coefficients distorts the image

drasticallydrastically

TheThe scaling factorscaling factor a is a critical system parameter.a is a critical system parameter. If a is tooIf a is too smallsmall. The image is not distorted but the robustness. The image is not distorted but the robustnessof the scheme is lowof the scheme is low

If a is tooIf a is too largelarge, the image is distorted but the robustness of the, the image is distorted but the robustness of the

scheme is highscheme is high Modification ofModification oflowlow--frequencyfrequency coefficientscoefficients Distorts the imageDistorts the image Gives the hacker a clue about where the watermark isGives the hacker a clue about where the watermark is

embeddedembedded Modification ofModification ofhighhigh--frequencyfrequency coefficientscoefficients

No distortionNo distortion TheThe watermakrwatermakr cannot be detected after attacks like JPEGcannot be detected after attacks like JPEG

compressioncompression

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ExamplesExamples InvisibleInvisible WatermarkingWatermarking

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ExampleExample 22 InvisibleInvisible WMWM

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VisibleVisible WatermarkingWatermarking

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BothBoth,, InvisibleInvisible andandVisibleVisible WMWM

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AttacksAttacks on WMon WM

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Audio WatermarkingAudio Watermarking

UsesUses DRM (Digital RightDRM (Digital Right ManamementManamement))

Proof of ownershipProof of ownership

Access control for digital mediaAccess control for digital media Tracing illegal copies Tracing illegal copies

Transmitting MetadataTransmitting Metadata

Like composer, soloist, genre of music,Like composer, soloist, genre of music,

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AudioAudio WatermarkingWatermarking

RequirementsRequirements Hidden, in case of music inaudibleHidden, in case of music inaudible

Statistically invisibleStatistically invisible

Robust against signal processing operationsRobust against signal processing operations

Directly connected to the music, not in aDirectly connected to the music, not in a

headerheader Key dependentKey dependent

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InaudibleInaudible Signals in Audio WMSignals in Audio WM

Temporal maskingTemporal masking 55--20ms before a loud signal20ms before a loud signal 5050--200ms after a loud signal200ms after a loud signal

A silent sound after a loud soundA silent sound after a loud sound Adding a echoAdding a echo

0 = 0.5ms after a sound0 = 0.5ms after a sound

1 = 1.0ms after a sound1 = 1.0ms after a sound MP3StegoMP3Stego

WAVWAV --> MPEG> MPEG--3 + additional Data3 + additional Data

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MP3StegoMP3Stego

Versteckter Text: Dies ist Alex sein File

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i.Ei.E:: GoogleGoogle ImagesearchImagesearch

WebcrawlerWebcrawler looking for Watermarkedlooking for Watermarkedpictures on Homepagespictures on Homepages

Money for PhotographersMoney for Photographers

MicrosoftsMicrosofts picturetankpicturetank

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QuestionsQuestions ??

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ThanksThanks forfor comingcoming!!!!