Digital watermark

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Digital Watermarking : 

Digital Watermarking Trailokya nath Sasamal M.Tech(DTI) Roll No-09305EN022 1

Agenda : 

Agenda Hierarchy of watermarking Watermark & Digital watermarking Steganography V/S watermarking Classification of watermarking Watermarking categories Watermarking Algorithm Watermarking Techniques Application 2

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3 (unique marks are embedded in copies of the carrier object)

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Steganography . Art of writing hidden messages Recipient knows the existence of the message Cryptography Message itself is not disguised, but the content is obscured Anybody can see that both parties are communicating in secret . 4 Message Existence secret Message contents secret

Steganography : 

Steganography Example: A German spy sent the following “harmless” message in WWII Apparently neutral’s protest is thoroughly discounted and ignored. Isman hard hit. Blockade issue affects pretext for embargo on by-products, ejecting suets and vegetable oils. 5

Steganography : 

Steganography If we extract the 2nd letter in each word, we get: Apparently neutral’s protest is thoroughly discounted and ignored. Isman hard hit. Blockade issue affects pretext for embargo on by-products, ejecting suets and vegetable oils. Or the secret message: Pershing sails from NY June 1. 6

An example : 

An example 7 AND

What is Watermarking? : 

What is Watermarking? Watermark Recognizable image or pattern in paper that appears lighter when viewed by transmitted light Watermarking The process of embedding information into another object/signal 8

Digital Watermarking : 

Digital Watermarking Technique which allows an individual to add hidden copyright notices or other verification messages to digital media Message is a group of bits describing information pertaining to the signal or its author Embedding of marks or labels that can be represented in bits in digital content Embedded marks are generally invisible (or imperceptible) but can be detected or extracted 9

Classification of Watermarks : 

Classification of Watermarks 10

A visible watermark : 

A visible watermark 11 taken from IBM research magazine

Invisible watermark : 

Invisible watermark 12

Invisible Watermark example : 

Invisible Watermark example 13

Steganography V/S watermarking : 

Steganography V/S watermarking watermarking the hiding data is used to protect the original image (e.g.copyright management) steganography the image is used to protect the hiding data (e.g. secret message). methods for hiding the existence of additional information in a cover signal. 14

Watermark Categories : 

Watermark Categories Robust Watermark Embedded invisible watermarks. Resist to image processing or attacks. Used for copyright protection or to verify the ownership. Fragile Watermark Destroy easily on modifying host signal Used for tamper detection Semi Fragile Watermark Sensitive to signal modification Feature of both robust & Fragile watermark. Provides data authentication 15

Types of Watermarking Algorithms : 

Types of Watermarking Algorithms Non Blind Use the original signal/image to extract embedded Watermark Semi Blind Don’t use the original signal Use side information and/or original watermark Blind Don’t use original signal or side information Most challenging 16

Watermarking Techniques : 

Watermarking Techniques Spatial Domain Watermarking Watermark embedded by modifying pixel values(for image) Spread spectrum approach Transform Domain Watermarking Watermark embedded in transform domain DCT, wavelet 17

Spread Spectrum Watermarking : 

Spread Spectrum Watermarking The watermark is transformed into a bit string b1b2….b64 For each bit bi, a pseudorandom matrix Ri of integers {1-1} is generated. 64 different matrices consisting pseudorandomly of {1 -1} Ri matrices depend on the bi of the watermark A matrix +Ri is used if bi represents a 0, A matrix -Ri is used if bi represent a 1 sum of all random patterns Ri defines the watermark W: W = watermarked image IW is generated by adding the watermark into cover image I IW = I + kW; 18

LSB substitution : 

LSB substitution Let wi be the ith bit of the watermark Let pj be the jth pixel of a cover image LSB substitution simply converts the least significant bit of pj to wi. Since only the LSBs are changed, the modification does not cause much perceptible noise to the cover. 19

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Replaces the N LSB planes of the cover image by the N MSB planes of the hidden image N= 4 bit hide Host Pixel: 10110001 New Image Pixel: 10110011 20 Secret Pixel: 00111111 Replace By

Robustness : 

Robustness LSB 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. 21

A DCT-based technique : 

A DCT-based technique Given a cover image, first decompose it into a number of 88 blocks. These squares is transformed via a DCT, which outputs a 2D array of 64 coefficients To encode bit value 0 make a mapping To store Bit 1 Make another mapping 22

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Another DCT-based technique : 

Another DCT-based technique pseudo noise to add a watermark to the DCT coefficients If the watermark contains n bits, use a secret key to locate n blocks at “pseudo-random” locations. The ith block Bi is used to carry the jth bit of the watermark, wj. large image can store some data that is quite difficult to detect in comparison to the LSB method. 24

Watermarking applications : 

Watermarking applications Ownership assertion – a rightful owner can retrieve the watermark from his content to prove his ownership. Fingerprinting – an owner can embed a watermark into his content that identifies the buyer of the copy (c.f. serial number). If unauthorized copies are found later, the owner can trace the origin of the illegal copies. 25

Watermarking applications : 

Watermarking applications Authentication – the creator of a content can embed a fragile watermark into the content to provide a proof of authenticity and integrity. Any tampering of the original content destroys the fragile watermark and thus can be detected. Visible watermarking – a visible watermark (an image) can be embedded on a “preview” to destroy its commercial value. 26

References : 

References Books Digital Watermarking :Ingemar Cox,Matthew Miller,Jeffrey Bloom MULTIMEDIA SECURITY TECHNOLOGIES FOR DIGITAL RIGHTS MANAGEMENT:Edited by: Wenjun Zeng, Heather Yu, Ching-Yung Lin Papers A Functional Taxonomy of Software Watermarking- Nagra,Thomborson,Collberg A TUTORIAL ON DIGITAL WATERMARKING-Fernando P´erez-Gonz´alez and Juan R. Hern´andez Collberg,Thomborson Software Watermarking: Models and Dynamic Embeddings G. Langelaar, I. Setyawan, and R. Lagendijk. Watermarking digital image and video data. IEEE Signal Processing Magazine, 17:20–46, 2000. [2] C. Rey and JL. Dugelay. A survey of watermarking algorithms for image authentication. EURASIP Journal on Applied Signal Processing, 6:613–621, 2002. F Hrtung M kultimedia (1999). “Watermarking techniquest”. Journal of Processding of the IEEE,Vol. 87, No. 7,pp.1079-1107. 27

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