

JPEG canaries: exposing on-the-fly recompression - bensummers
http://www.lightbluetouchpaper.org/2011/02/04/jpeg-copy-evidence/

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KingOfB
_to cause maximum quantization error on recompression at a chosen target JPEG
quality factor_

Neat, but pretty worthless in the domain explained though isn't it? Exposing
re-compressing proxies? So if your float for re-compression matches their
float for re-compression, you'll see a slightly blurry word!

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slavak
Like someone commented on the site itself, I also can see a faint outline of
the hidden message in the original (left) image. It changes in clarity if I
change the angle I'm viewing my LCD screen at - most visible when I view it
from below (which darkens the screen).

~~~
jarin
It also changes from visible to invisible if you scroll one pixel up or down
(although this may depend on your monitor).

I suspect though that it would be almost impossible to detect on a photo (the
typical use case for JPEGs).

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limmeau
Just tried it out with Opera Turbo enabled: both pictures have a similar
moiree-like pattern, with "VOID" on neither.

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TheAmazingIdiot
Hmm.

There was an article (of all places) on /b/ on explicitly how to manipulate
compression filters to display 2 completely different images within the error
domains that make the word "void" express. 1 or 2 people were actually
publishing code in /b/'s conversation explaining how to repeat and why this
happened.

However, they were using this algorithm to hide animated child porn and other
just plain nasty stuff, but they were discussing it all right. If prodded, I
could provide links. But I wont be held responsible for the disgust resulting.

~~~
coderdude
If you don't end up posting the links, please send them to me in an email. I'd
like to see that code and the explanation behind it.

~~~
TheAmazingIdiot
Unfortunately the link to the FAQ that specifically talked about 4chan's
scaling is a dead link now.

I'm currently looking there and asking to see if anybody remembers what its
called, and where the FAQ is. It was how to make these in photoshop

I WILL be posting here, to this thread when I have information about it.

Do not open these files unless you are in a secure location in a private area.
It's nasty, but it's what links /b/ could provide.

    
    
         _______________________________________________________
         WARNING - WARNING - WARNING
    
         http://img831.imageshack.us/img831/7619/1297043379628.png
         http://img130.imageshack.us/img130/2484/1297043089626.png
         http://img703.imageshack.us/img703/318/1297042904730.png

~~~
coderdude
Well if all that's left are the child porn pics... I think we can pass on
them. Thanks for looking for the thread though.

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derleth
I can see the 'VOID' in the original image as well. I wonder what kind of
problems that's going to cause if this gets out into the wild.

~~~
limmeau
Are you behind a compressing proxy (e.g. Opera Turbo)?

~~~
derleth
Not to the best of my knowledge; certainly, no such thing is running on my
system.

The point is, most people would have absolutely no idea of how to even begin
answering that question. If you teach them that 'VOID is Bad' and then your
legitimate images have 'VOID' on them, it's going to cause problems and you're
not going to be able to educate them well enough, fast enough.

~~~
limmeau
Agree. As for the proxying: Vodafone uses a transparent proxy on their UMTS
network[1], other mobile companies might, too.

1\. [http://www.yetanotherblog.com/2007/08/20/vodafone-
transparen...](http://www.yetanotherblog.com/2007/08/20/vodafone-transparent-
proxy-bmi-javascript-at-1234/)

