Abstract: 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.
@article{Lewis:2009,
url = {http://www.cl.cam.ac.uk/~abl26/info09-jpeg.pdf},
journal = {Lecture Notes in informatics},
author = {Andrew B. Lewis and Markus G. Kuhn},
year = {2009},
title = {Towards copy-evident {JPEG} images},
}