Steganography and Digital Watermarking

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Steganography and Digital Watermarking
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• Prisoners Problem
• Michael Scofield and Lincoln Burrows are in jail
• They want to develop an escape plan
• The only way to communicate is through Captain
  Bellick
• They must communicate in a manner that does not
  raise suspicion

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THE LEADER

• Patient and steady with all he must bear,
• Ready to meet every challenge with care,
• Easy in manner, yet solid as steel,
• Strong in his faith, refreshingly real.
• Isn't afraid to propose what is bold,
• Doesn't conform to the usual mould,
• Eyes that have foresight, for hindsight won't do,
  
• Never backs down when he sees what is true,
• Tells it all straight, and means it all too.
• Going forward and knowing he's right,
• Even when doubted for why he would fight,
• Over and over he makes his case clear,
• Reaching to touch the ones who won't hear.
• Growing in strength he won't be unnerved,
• Ever assuring he'll stand by his word.
• Wanting the world to join his firm stand,
• Bracing for war, but praying for peace,
• Using his power so evil will cease,
• So much a leader and worthy of trust,

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PatchworkBender, Gruhl, Morimoto and Lu

• Choose any 2 random points A and B
• ai , bi be the luminance of A and B
• S ai - bi
• Summing S for large n
• Sn ?i1n (ai - bi )
• Sn is approx 0 because for large n
• The pixels are independent and identically
  distributed
• The no of times ai gt bi and bi gt ai
  should be roughly same for large n

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Patchwork continuedBender, Gruhl, Morimoto and
Lu

• communicating parties share a key k
• Choose A, B pseudo randomly based on k
• Raise the brightness in ai by 1
• Lower the brightness in bi by 1
• ai ai 1
• bi bi - 1
• Sn ?i1n (ai 1 (bi 1) )
• Sn ?i1n (ai - bi ) ?i1n 2
• Sn is approximately 2n
• because ?i1n (ai - bi ) approx 0 for
  large n

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Conditions for watermarking

• Keep in mind the following considerations before
  embedding a digital watermark in your image.
• Color variation
• The image must contain some degree of variation
  or randomness in color to embed the watermark
  effectively and imperceptibly. The image cannot
  consist mostly or entirely of a single flat
  color.
• Pixel dimensions
• The Digimarc technology requires a minimum
  number of pixels to work. Digimarc recommends the
  following minimum pixel dimensions for the image
  to be watermarked
• 100 pixels by 100 pixels if you don't expect the
  image to be modified or compressed prior to its
  actual use.
• 256 pixels by 256 pixels if you expect the image
  to be cropped, rotated, compressed, or otherwise
  modified after watermarking.
• 750 pixels by 750 pixels if you expect the image
  to appear ultimately in printed form at 300 dpi
  or greater.
• There is no upper limit on pixel dimensions for
  watermarking.