Digital Digital WatermarkingWatermarking

Alexander Hasslacher, 0056448Alexander Hasslacher, 0056448

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

WhatWhat isis a a WatermarkWatermark

EncoderOriginal Image (I)

Signatur (S)

Watermarked Image (I‘)

TypesTypes of Digital of Digital WatermarksWatermarks

VisibleVisible and and invisibleinvisible WatermarkWatermark

LSB LSB 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

FFT, DCTFFT, DCT

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

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ConclusionsConclusions•• Modification of Modification of allall DCT coefficients distorts the image DCT coefficients distorts the image

drasticallydrastically•• The The scaling factorscaling factor a is a critical system parameter.a is a critical system parameter.

–– If a is too If a is too smallsmall. The image is not distorted but the robustness . The image is not distorted but the robustness of the scheme is lowof the scheme is low

–– If a is too If 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 of Modification of lowlow--frequencyfrequency coefficientscoefficients–– Distorts the imageDistorts the image–– Gives the hacker a clue about where the watermark is Gives the hacker a clue about where the watermark is

embeddedembedded•• Modification of Modification of highhigh--frequencyfrequency coefficientscoefficients

–– No distortionNo distortion–– The The watermakrwatermakr cannot be detected after attacks like JPEG cannot be detected after attacks like JPEG

compressioncompression

ExamplesExamples InvisibleInvisible WatermarkingWatermarking

ExampleExample 2 2 InvisibleInvisible WMWM

VisibleVisible WatermarkingWatermarking

BothBoth, , InvisibleInvisible and and VisibleVisible WMWM

AttacksAttacks on WMon WM

Audio WatermarkingAudio Watermarking

•• UsesUses–– DRM (Digital Right DRM (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,…

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

headerheader–– Key dependentKey dependent

InaudibleInaudible Signals in Audio WMSignals in Audio WM

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

•• A silent sound after a loud sound A 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

•• MP3Stego MP3Stego –– WAV WAV --> MPEG> MPEG--3 + additional Data3 + additional Data

MP3StegoMP3Stego

Versteckter Text: Dies ist Alex sein File

i.Ei.E: : GoogleGoogle ImagesearchImagesearch

•• WebcrawlerWebcrawler looking for Watermarked looking for Watermarked pictures on Homepagespictures on Homepages

•• Money for PhotographersMoney for Photographers•• Microsoft´sMicrosoft´s picturetankpicturetank

QuestionsQuestions ??

Thank´sThank´s forfor comingcoming!!!!