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Watermark Description by Ravi Sharma

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  2. 2. Content What is watermarking History Digital Watermarking Classification Visible And Invisible Watermarking Text And Image Watermarking Examples, Techniques And Applications 2
  3. 3. What is Watermarking A watermark is a recognizable image or pattern in paper that appears as various shades of lightness/darkness when viewed by transmitted light (or when viewed by reflected light, a top a dark background), caused by thickness variations in the paper. 3
  4. 4. Watermarking History More than 700 years ago, watermarks were used in Italy to indicate the paper brand and the mill that produced it. By the 18th century watermarks began to be used as anticounterfeiting measures on money and other documents. The term watermark was introduced near the end of the 18th century. It was probably given because the marks resemble the effects of water on paper The first example of a technology similar to digital watermarking is a patent filed in 1954 by Emil Hembrooke for identifying music works. In 1988, Komatsu and Tominaga appear to be the first to use 4 the term “digital watermarking”.
  5. 5. Paper WatermarksPaper Watermarks: Formed during the manufacturingprocess of the paper when the paper is wet, so that fiberscan be disturbed according to the design of the watermark.Used mainly for identification and authentication 5
  6. 6. Digital WatermarkingDefinition: A digital watermark is a digital signal or patterninserted into a digital document such as text, graphics ormultimedia, and carries information unique to the copyrightowner, the creator of the document or the authorizedconsumer. 6
  7. 7. Common Examples Currency Notes Stamps Passports Legal Documents Logos used by cable TV channels 7
  8. 8. Currency Notes 8
  9. 9. Watermark Example 9
  10. 10. Watermark Example 10
  11. 11. Example 11
  12. 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 12
  13. 13. Visible Watermarking In visible watermarking, the information is visible in the picture or video. Typically, the information is text or a logo which identifies the owner of the media. When a television broadcaster adds its logo to the corner of transmitted video, this is also a visible watermark. 13
  14. 14. Visible Watermarking + = 14
  15. 15. Invisible Watermarking In invisible watermarking, information is added as digital data to audio, picture or video, but it cannot be perceived as such (although it may be possible to detect that some amount of information is hidden). It is also possible to use hidden embedded information as a means of covert communication between individuals. 15
  16. 16. Small changes in brightness,contrast, etc. (sail_e.jpg): Signed image. Verify (sail.jpg): Original image. with secret key 100001. 16
  17. 17. Watermarking Process 17
  18. 18. Basic Principle 18
  19. 19. 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. 19
  20. 20. Text line coding example 20
  21. 21. Word-shift coding example 21
  22. 22. 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. 22
  23. 23. Example 23
  24. 24. Example Original Watermarked Version 24
  25. 25. Watermarking Attacks Signal enhancement (sharpening, contrast enhancement, etc.) Additive and multiplicative noise (gaussian, uniform, etc.) Filtering (High pass, low pass, linear, nonlinear, etc.) Lossy compression (JPEG, MPEG-x, H.26x, etc.) Geometric transforms (translation, rotation, etc.) Data reduction (cropping, clipping, etc.) Transcoding (MPEG2 ⇒ H.263, etc.) D/A and A/D conversion (print-scan, etc.) Multiple watermarking Collusion attack 25
  26. 26. Multiple watermarking 26
  27. 27. Characteristics of Digital Watermarks Unobtrusive: invisible enough not to degrade the data quality and to prevent an attacker from finding and deleting it. Readily Detectable: the data owner or an independent control authority should easily detect it. Unambiguous: retrieval of it should unambiguously identify the data owner. Innumerable: it should be possible to generate a large number of watermarks, all distinguishable. 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. 27
  28. 28. Applications Embed information about the owner to prevent others from claiming copyright For example, a compliant DVD player will not playback or copy data that carry a “copy never” watermark This is useful to monitor or trace back illegally produced copies of the cover Used to avoid unauthorized duplication and distribution. Digital watermark inserted to indicate the number of copies permitted. 28
  29. 29. Thank You