From: Bill Stewart <stewarts@ix.netcom.com>
Date: Tue, 24 Jun 1997 14:51:39 +0800
To: cypherpunks@Algebra.COM
Subject: Re: Sources for stego images, was re: Laying PipeNet
In-Reply-To: <v03102804afd38b324730@[10.0.2.15]>
Message-ID: <3.0.2.32.19970623233825.03113e3c@popd.ix.netcom.com>
MIME-Version: 1.0
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>> >That's the major problem with images, you need to generate your own.
>> >Unless you fancy writing an image enhancement system, and analyse the
>> >algorithms in existing systems to ensure that randomness is
>> >introduced.
..
>Or, set up your own webcam "to watch your coffee pot twice a minute" or
>something. Merge the crypto stream through the gifs after tweaking the
>brightness and contrast to avoid 0 and 255 (a light fixture with a pattern
>of 254/255 values gets suspicious, and is not from thermal noise - a
>"problem" with monochrome quickcams for night photography).

Pictures like coffee pots are likely to have parts that change
(e.g. the state of the coffee pot) and parts that don't change 
(e.g. the part of the wall that isn't blocked by the pot.)
This means that it's easy to tell which bits are being messed with,
if somebody's watching successive pictures.  If the digitization's
random enough in the low bits, it's a bit better, but a picture of
something moving helps.  Oceans and fog are great....


#			Thanks;  Bill
# Bill Stewart, +1-415-442-2215 stewarts@ix.netcom.com
# You can get PGP outside the US at ftp.ox.ac.uk/pub/crypto/pgp
#   (If this is a mailing list or news, please Cc: me on replies.  Thanks.)