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2. Outline
 Introduction, Applications
 Characteristics and classification
 Popular techniques for watermarking
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3. Definition: A digital watermark is a
digital signal or pattern inserted into a
digital document such as text, graphics
or multimedia, and carries information
unique to the copyright owner, the
creator of the document or the
authorized consumer.
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4. Example
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5. Watermarking Vs Encryption
 Encryption involves document transformation so that
the contents of the document are not visible without
a decryption key
 Watermarking leaves the original file/image intact
and recognizable
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7. Digital Watermarking Applications
 Ownership Assertion
 ‘A’ uses a private key to generate a watermark and embeds it in the
document
 ‘A’ makes the watermarked image publicly available
 ‘B’ claims that he owns the image derived from the public image
 ‘A’ produces the unmarked original and establishes the presence of ‘A’s
watermark
 Fingerprinting
 Used to avoid unauthorized duplication and distribution.
 A distinct watermark (a fingerprint) is embedded in each copy of the data.
 If unauthorized copies are found, the origin of the copy can be determined
by retrieving the fingerprint.
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8. Digital Watermarking Applications (2)
 Authentication & integrity verification
 Watermarks should be able to detect even the slightest
change in the document.
 A unique key associated with the source is used the
create the watermark and then embed in the document.
 This key is then used to extract the watermark and the
integrity of the document verified on the basis of the
integrity of the watermark.
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9. Digital Watermarking Applications (3)
 Content labeling
 Bits embedded in the data, comprise an annotation,
giving some more information about the data.
 Digital cameras annotate images with the time and
date, when the photograph was taken.
 Medical imaging machines annotate images (X-Rays)
with patients name, ID.
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10. Digital Watermarking Applications (4)
 Usage control & Copy protection
 Digital watermark inserted to indicate the number of
copies permitted.
 Every time a copy is made the hardware modifies the
watermark and at the same time it would not create any
more copies of the data.
 Commonly used in DVD technology.
 Content Protection
 Content owner might want to publicly and freely
provide a preview of multimedia content being sold.
 To make the preview commercially useless, content is
stamped with visible watermarks.
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11. Characteristics of Digital Watermarks
 Readily Detectable: the data owner or an independent control authority
should easily detect it.
 Unambiguous: retrieval of it should unambiguously identify the data
owner.
 Robust: difficult to remove for an attacker, who would like to
destroy it in order to counterfeit the copyright of the data.
Moreover, removal of it should cause a considerable degradation
in the quality of the data.
 Visible watermarks should be visible enough to discourage theft.
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12. Digital Watermark
Classification
 Based on visibility of watermarks
- Visible Watermarks
- Invisible Watermarks
 Based on the content to be watermarked
- Text Watermarking
- Image, Audio, Video Watermarking
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13. Techniques for Texts
Text Line Coding: Change the spacing
between lines.
Word-shift Coding: Change the spacing
between words.
Character Encoding: Alter the shapes of
characters.
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15. Word-shift coding example
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16. Easily defeated…
 Retyping the text destroys the watermark
 Word processors change the spacing between
words and lines
 Character encoding can be defeated by changing
the font
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17. Techniques for Images
 Spatial Watermarking: Just change some of the values of the
pixels in the lower bit plane; e.g., Change some of the bits from 1
to 0 or 0 to 1.
 Frequency Domain Watermarking: First convert the image to the
frequency domain and then apply the watermark in the low
frequency regions.
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18. Checksum Technique for images
 Watermark is formed from the 7 most significant bits of each pixel.
 Eight 7-bit segments (from eight different pixels) are concatenated
and the final checksum is thus 56-bit.
 Locations of the pixels that are to contain one bit each of the
checksum are randomly chosen.
 These pixel locations along with the checksum form the watermark,
W.
 Last bit of each pixel is then changed to the corresponding checksum
bit.
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20. Bavarian couple
Original Watermarked Version
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21. Advantages/Disadvantages
 Embedding the checksum only changes (on average) half the number
of pixel. So less visual distortion.
 Can hold multiple watermarks as long as they don’t overlap.
 Extremely simple and fast.
 Extremely fragile. Any change to the checksum causes the failure of
the verification procedure.
 Forger could replace a section with another one of equal size and
checksum.
 Entire watermark can be removed by removing the LSB plane. Can’t
survive lossy compression.
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22. Conclusion
 First generation of copyright marking schemes is not
strong enough
 Existing schemes provide only limited measures of
marking
 Can only meet few requirements at a time
 Tradeoff - Bandwidth vs. robustness
 No single problem but a constellation!
 Real problem: watermark restoration
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23. Q&A
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