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New Technique For Making JPEG Images Copy-Evident
Gunkerty Jeb writes "The days of wondering whether those drunken sex party photos are indeed the Olsen Twins, or if they are just the Mary-Kate and Ashley's faces photo-shopped on the bodies of Lindsay Lohan and Amy Winehouse are OVER! A group of academic researchers at the University of Cambridge has developed a new technique for making JPEG images copy-evident, so that users can tell whether an image has been recompressed and copied."
If the image can't be re-encoded or re-scaled without the watermark becoming visible, then it probably can't be resized for viewing either. So the only images can can really make use of this 'tech' are the ones that are already shrunk to their smallest desirable viewing size. I'm not sure how much use this will really have.
From the original paper: "The technique now needs to be extended to handle arbitrary photographs, not just uniform regions."
Nice try at getting fast karma from a first post, but that's not going to work. The screen shot will already be of the compressed image, and will still show signs of re-compressing it.
If you're really serious about putting Mary Kate and Ashley's head on Lindsay Lohan and Amy Winehouse's bodies, like it says in TFS, you'd use RAW. Then, you can compress everything together. Besides, if you upload that to photo sharing websites (especially Facebook) there's a high chance your picture would be recompressed, so it would have the compression artifacts whether it's been altered or not.
Fail.
Have access to RAW files of the aforementioned act involving Lindsay and Amy, along with ideally angled shots of the Olsen's faces? Didn't think so. So, you go to google images and start digging. What you find (in the ideal world this paper is picturing (ugh no pun intended)) is that every content creator (from the pr0n guys to the papparazzi that took the olsen's picture) have applied this filter to their work, and as such your efforts are for not. Don't get me wrong, there are tons of problems with this whole idea, but saying "well raw doesnt have artifacts anyway" is a bit of a fail.
So I downloaded their test image here: http://www.cl.cam.ac.uk/~abl26/copy-google.jpg that they claim gets a message on it when compressed by google proxy http://www.google.com/gwt/x/i?u=http%3A%2F%2Fwww.cl.cam.ac.uk/~abl26/copy-google.jpg&wsi=223e8e5df695e99c&ei=6ixQTebOCoPoxQW8rYlv&wsc=yq&whp=012e012f72be
But when I take the original and re-save it in Photoshop CS5 I don't see the void lettering. I reduced the JPEG quality and kept trying and at quality 1, the lowest setting I was starting to see a pattern, but no words appeared.
I'd say their idea is nice, but doomed to failure, not least they mention "If you can’t see the message in the recompressed image, make sure your browser is rendering the images without scaling or filtering." which would be the obvious source of attack on such a method should it actually work in practise.
-- oldthinkers unbellyfeel ingsoc
(keys desk intercom) Miss Jones, come in here! And bring your steganography pad!
No folly is more costly than the folly of intolerant idealism. - Winston Churchill
If you read the article, they are depending on the JPEG compression artifacts for the watermark display. Resizing should not cause this because you are deling with the uncompressed image data.
Resizing and then saving as a JPEG will result in re-compression and the watermark appearing. Saving as anything else bypasses this completely.
This is only useful when you know what conditions will be applied. The example they give near the end, uploading to youtube, will apply only as long as youtube does not change their settings. Then you have to change your thresholds and all of your protected videos in the wold are unprotected.