waterm tut
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Example:LSB Encoding
Original Image Watermark
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Replace 4 and 7 LSBs of Original
4 LSBs Watermarked 7 LSBs Watermarked
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What is a Watermark?
A watermark is a secret message that is embedded
into a cover (original or host) message.
Only the knowledge of a secret key allows us toextract the watermark from the cover message.
Effectiveness of a watermarking algorithm is a
function of its
Resilience to attacks.
Capacity.
Stealth.
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What Can Be Watermarked?
Multimedia data.
Video.
Audio. Still Images.
Documents.
Software.
Hardware designs.
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Watermark Applications
Proof of ownership. Prove ownership in a court of law.
Simple copyright notice may not help for digitalmultimedia data. Easily destroyed.
Copy prevention or control. Recording device may inhibit recording a signal if
detected watermark indicates that it is prohibited.
DVD video and digital music distribution.
Content protection (visible watermarks). Destruction of watermark destroys the content.
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Watermark Applications
Authentication. Detect if image/video has been altered.
Digital cameras.
Media Bridging. Bridge media such as magazines and the Internet.
Digimarc.
Broadcast Monitoring. Keep track of when and where an advertisementis played.
ConfirMedia from Verance.
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Watermark Applications
Fingerprinting. Identify the source of an illegal copy.
Unique watermark embedded in each copy.
DiVX, a modified version of DVD.
Secret Communications.
Hide information such that general public do not
know its presence.
Bin Laden hides attack plans in images on the
web USA Today, Feb. 26, 2001.
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Requirements
Requirements vary with application. For
example:
Perceptually transparent - must not perceptuallydegrade original content.
Robust - survive accidental or malicious attempts
at removal.
O
blivious or Non-oblivious - Recoverable with orwithout access to original.
Capacity Number of watermark bits embedded.
Efficient encoding and/or decoding.
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Contradicting Requirements
Perceptual Transparency
Oblivious vs. Non-Oblivious
RobustnessPayload Security
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Example: Additive Watermarks
W( , ) : seudo and om attern {-1,0,1}
kMultiply by gain
factork
I( , ) IW( , )
IW(x,y)=I(x,y)+k W(x,y)
W(x,y) detected
T p
' ( , ) ( , )W
I x y W x yR T" p
No W(x,y) detected
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h
v
Additive watermarks in transformdomain: Spread Spectrum
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Watermark Attacks
Active Attacks.
Hacker attempts to remove or destroy the
watermark. Watermark detector unable to detect watermark.
Key issue in proof of ownership, fingerprinting,
copy control.
Not serious for authentication or covertcommunication.
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Watermark Attacks
Passive Attacks. Hacker tries to find if a watermark is present.
Removal of watermark is not an aim. Serious for covert communications.
Collusion Attacks. Hacker uses several copies of watermarked data
(images, video etc.) to construct a copy with nowatermark.
Uses several copies to find the watermark.
Serious for fingerprinting applications.
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Watermark Attacks
Forgery Attacks.
Hacker tries to embed a valid watermark.
Serious in authentication. If hacker embeds a valid authentication
watermark, watermark detector can accept bogus
or modified media.
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Example: Forging Photo I.D.
Bad
Forgery!
Millionaire with
Swiss bank
account
Assistant
Professor
Thanks
Hong Man,
for this
picture!
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Content-based Watermarking
Original Watermark
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JPEG Compression Attack
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Watermarking Research
Information Theoretic Issues. Compute watermarking capacity
How many watermark bits can be hidden in awatermark channel ?
Capacity when multiple watermarks are used.
Decision Theoretic Issues. Robust watermark detector.
Quickest possible watermark detection.
Invariant to statistical uncertainties.
Achieves desired false alarm and detectionprobabilities.
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Watermarking Research
Signal Processing Issues. What transforms to use ? wavelet, DCT etc.
Geometric invariant transform scale, translation,
and rotation invariance. Watermarking protocols and system issues.
Protocol used by sender and receiver for securetransmission.
Steganalysis. How to analyze multimedia data for the presence
of watermark(s).
Secure Digital Music Initiative (SDMI) has beenhacked!
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Robust Watermarking Techniques- A Communications Framework
+
Media Carrier
HVS
Watermark
Media Carrier
Noise/Attack Channel
Water-
mark
Coding and
Modulation
Decoding and
DemodulationX
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Techniques Developed at
MSyNC Lab
(some results are in collaboration with
Iowa State U. and Polytechnic U.)
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Information TheoreticFormulation
A new watermark channel model. Multiplicative and additive attacks.
Models geometric attacks (killer attack).
Attack parameters assumed imperfectlyknown.
Lower and upper bounds on watermarkingcapacity.
Many current capacity estimates are specificcases of proposed estimates.
Capacity in the presence of multiplewatermarks using multiuser information
theory.
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Multiple DescriptionWatermarking
A new framework for watermarking using
multiple description codes.
Partition the source into multiple descriptions. Each description carries enough information.
Allocate watermarking bits to descriptions subject
to distortion constraints.
Experiments for secure wireless mediatransmission is promising.
Rate-distortion theory formulation.
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Decision Theoretic Formulation
How many pixels to watermark ?
A new measure for watermarking capacity.
Different from standard information theoreticformulation.
Perhaps a more practical measure.
Fast watermark detector.
Computation reduction. Useful for hardware implementation.
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Steganalysis
A distributed detection framework for
analyzing images for presence of
watermarks. Theoretical formulation and practical
algorithm for steganalysis of LSB based
image watermarking.
A new watermarking capacity measure calledsteganographic capacity.
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Projected Applications ofProposed Techniques
Secure media streaming.
Wireless multimedia security.
Watermark error resilience coding.
Error concealment for wireless multimedia
transmission. Refer to
http://www.ece.stevens-tech.edu/~mouli/msync/index.html
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Million Dollar Question
Watermarking or Encryption or Combination?