From: wcs@anchor.ho.att.com (bill.stewart@pleasantonca.ncr.com +1-510-484-6204)
Date: Tue, 1 Mar 94 14:39:49 PST
To: cypherpunks@toad.com
Subject: Re: stego
Message-ID: <9403012217.AA05764@anchor.ho.att.com>
MIME-Version: 1.0
Content-Type: text/plain


Jim Choate's comments on steganography having problems with images
that are too complex or too simple were interesting.
Obviously, cartoon-like GIFs aren't a good target, though scanned
real stuff may be fine.  Weather maps cna be good - back when I worked
with the things, I found you could really see about5-6 bits worth of
depth, and after that it didn't usually look much different -
we stole one or two values from the color-map to draw lines on
the satellite images to add state boundaries, various data values, etc.,
but could have stolen the LSB and maybe 7th bit without major loss on
cloud-image pictures.  (Radar pictures, on the other hand, were almost
all black, with one or two other pixel values, compressed to 2% of original
size, and would have been useless for hiding anything in.)

		Bill