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Towards copy-evident JPEG images

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Practice talk for Informatik 2009

We present a technique for adding a high-frequency pattern to JPEG images that is imperceptible to the unaided eye, but turns into a clearly 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 result of the inverse discrete cosine transform.

This talk is part of the Computer Laboratory Security Group meeting presentations series.

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