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SUMMARY:Towards copy-evident JPEG images - Andrew Lewis (University of Cam
 bridge)
DTSTART:20090925T150000Z
DTEND:20090925T153000Z
UID:TALK20363@talks.cam.ac.uk
CONTACT:Markus Kuhn
DESCRIPTION:We present a technique for adding a high-frequency pattern to 
 JPEG images that is imperceptible to the unaided eye\, but turns into a cl
 early readable large-letter warning if the image is recompressed with some
  different quality factor. Our technique aims to achieve a goal similar to
  copy-evident security-printing techniques for paper documents\, namely to
  have an easily recognizable text message appear in lower-quality copies\,
  while leaving the visual appearance of the original unharmed. We exploit 
 non-linearities in the JPEG process\, in particular the clipping of the re
 sult of the inverse discrete cosine transform.
LOCATION:Computer Laboratory\, William Gates Building\, Room FW11
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