From: Harvey Newstrom (mail@HarveyNewstrom.com)
Date: Thu Oct 11 2001 - 10:35:40 MDT
Terry W. Colvin asked,
> Is there visual noise in photos similar to communications circuits always
> transmitting and receiving?
Newer equipment does not produce much if any noise. Photographers take
multiple photographs to get a good one. Modern equipment eliminates noise.
Digital image files can be edited to remove noise. Compression and
smoothing technologies also remove noise. Therefore, most pictures stored
digitally should be almost perfect, with all noise removed and with
efficient compression. Such technology is pretty much standard in Windows
and most share-ware programs. Anybody sending poor quality pictures with
lots of noise would be in the minority.
Therefore, a large fraction of Internet pictures can be eliminated just be
the sheer fact that they have little noise. Noise also has predictable
patterns for known blur, film, scanner and software corruptions. These can
also be weeded out easily with a computer program that has a database of
image scanning patterns. Imagine have a database of how every known
commercial software or shareware encodes images. Then you find an image
that was created by an unknown program. This would be very rare and
immediately suspect.
All that remains for hiding messages is poor-quality, high noise images
produced by non-standard or home-written software. Since most people have a
standard OS with standard software, these relatively obscure images become
even more unique in the population.
Also, counter-intuitively, adding noise actually makes it *easier* to
eliminate the noise. The more noise there is, the more statistically
predictable it becomes. Statistical analysis works better the more sample
you have. Lots of static over a longer period of time actually makes it
easier to eliminate the static.
-- Harvey Newstrom <www.HarveyNewstrom.com> Principal Security Consultant, Newstaff Inc. <www.Newstaff.com> Board of Directors, Extropy Institute <www.Extropy.org> Cofounder, Pro-Act <www.ProgressAction.org>
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