Watermarking, steganography and content forensics - · PDF fileWatermarking Steganography Content forensics 2. Ingemar J. Cox Watermarking Watermarking is the practice of imperceptibly

Watermarking, steganography and content forensics

Ingemar J. Cox

Ingemar J. Cox

Introduction

Watermarking

Steganography

Content forensics

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Watermarking

Watermarking is the practice of imperceptibly altering a Work (image, song, etc.) to embed a

message about that Work.

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Watermarking

The primary motivation for watermarking has been to protect content

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Muzak: the first commercial watermarking

The first skyscraper was built in Chicago in 1885

Ingemar J. Cox

Muzak: the first commercial watermarking

The elevator was an essential element

In the 1930s passenger elevators were new and frightening Music in elevators was introduced to calm passengers

Muzak was the dominant supplier

Nirvana - On a plain

Rockabye Baby - On a plain

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Muzak: the first commercial watermarking

The elevator was an essential element

In the 1930s passenger elevators were new and frightening Music in elevators was introduced to calm passengers

Muzak was the dominant supplier

Nirvana - On a plain

Rockabye Baby - On a plain

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Muzak: the first commercial watermarking

The elevator was an essential element

In the 1930s passenger elevators were new and frightening Music in elevators was introduced to calm passengers

Muzak was the dominant supplier

Nirvana - On a plain

Rockabye Baby - On a plain

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Muzak: the first commercial watermarking

Emil Hembrooke, Identification of sound and like signals, US Patent 3,004,104 Filed 1954, Issued 1961

The present invention makes possible the positive identification of the origin of a musical presentation and thereby constitutes an effective means of preventing such piracy, i.e. it can be likened to a watermark in paper.

In use until the mid 1980s

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Applications of digital watermarking

Broadcast Monitoring Nielsen/Digimarc Teletrax/Philips

Owner Identification Verimatrix - IPTV Widevine Technologies

Proof of Ownership

Transaction Tracking Thomson/Technicolor (Philips) - Oscar screeners Cinea/Dolby - Digital cinema

Ingemar J. Cox

Applications of digital watermarking

Content Authentication Signum Technologies

Copy Control Verance - HD-DVD, DVD-audio

Legacy systems Tektronix - syncing sound and video (lipsync) MarkAny - syncing lyrics with music (mp3 players)

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Watermarking

Why not use cryptography?

Cryptography assumes:1. Alice and Bob trust one another2. Communication between Alice and Bob succeeds

However, Alice (Hollywood) cannot trust Bob (consumer) And if communication fails, watermark protection fails

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Watermarking

Watermarking is NOT cryptography

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Watermarking

Watermarking IS communications

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Watermarking

The content is more important than the message

So the watermark/message must be imperceptible

And often, the message payload is small

But, to be practical, a watermark must also be robust

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Watermarking

Spread spectrum communications content modeled as noise

high noise regime

Communications with side information content modeled as side information

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Watermarking as communications

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Transmitter Receiver+

Noise

message, mmessage, m x y

x is limited by a power constraint x2[i] p

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Watermarking as communications

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Embedder Detector

Noise

message, m message, mx y+ +

Noise

x is limited by a power constraint x2[i] p

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Spread spectrum communications

Requirements: Unobtrusive Survive common distortions

E.g. lossy compression

Spread spectrum communications Originally developed for military communications

Difficult for enemy to detect Difficult for enemy to jam

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Spread spectrum communications

Lets consider embedding an 8-bit message in an image 01100101

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Spread spectrum communications

Since we have an 8-bit message Spread each bit over all pixels

Spread spectrum watermarking

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Spread spectrum communications

Each bit is represented by a chip sequence A pseudo random number sequence

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Spread spectrum communications

10 101 0 1 0

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Spread spectrum communications

Detect each bit using linear correlation

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Spread spectrum communications

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Spread spectrum communications

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Spread spectrum communications

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Spread spectrum communications

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Spread spectrum communications

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Spread spectrum communications

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Spread spectrum communications

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Spread spectrum communications

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Spread spectrum communications

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Perceptual modelling

In the previous example, the random pattern was added equally to all parts of the image

But some areas are more (less) sensitive than others

We can identify these areas using perceptual models Same models used for lossy compression

Must embed in perceptually SIGNIFICANT regions to be robust to lossy compression

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Original image

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No perceptual modeling

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Perceptual modeling

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Original image

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Communications with side information

Spread spectrum watermarking models the cover Work as noise

However, the cover Work is Not random Completely known at the time of embedding

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Watermarking as communications

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Embedder Detector

Noise

message, m message, mx y+ +

Noise

x is limited by a power constraint x2[i] p

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Watermarking as communications

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Embedder Detector

Noise

message, m message, mx y+ +

Noise

x is limited by a power constraint x2[i] p

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