NOTE: This message is being cross-posted to both amavis-user
and
devel-spam.
Lately, there has been quite a bit of discussion about
animated GIFs (also
APNGs) and how to scan them for SPAM. This discussion is
taking place on
the FuzzyOCR mailing list:
http://lists.own-hero.net/mailman/listinfo/devel-spam
The result of which has become a very technical discussion
about frame
selection and scanning. As most of you probably realize
there are two
primary challenges right now with image spam: One is the use
of animation
techniques to obscure the SPAM message and make it difficult
to find. The
second is devising a strategy to fight the use of
OCR-fooling techniques
and adapting the techniques we've learned from text SPAM.
For those of us that are willing, it would be wonderful to
reduce the
struggle to only one. Specifically, a mail administrator
should be able to
respond to or impose organizational mail policies regarding
animated
GIFs/APNGs at the mail-server level.
Let's get to the point:
It would be great to be able to "flatten" or
"display-the-last-frame" or
eliminate completely any animated graphic format as an
option in
amavisd-new.
This would involve:
- a configuration option in amavisd.conf (filter, flatten,
last-frame)
- performing a simple check to test for the use of animation
in an inline
graphic (there only two formats that I am aware of right now
-- GIF, APNG)
- calling of an external helper program such as gifsicle or
ImageMagik to
alter the inline image (or remove it) within the e-mail
Knowing that animated images have been handled, we can
significantly reduce
the amount of work that plugins like FuzzyOCR have to
perform. For
example, no "deoptimizing" of frames would have to
be performed at the
scanner level, no complex frame selection algorithm would be
needed, and
only one OCR scan would be necessary (hopefully).
Of course, this functionailty of FuzzyOCR would still be
optionally
available for those that need or want animated graphics in
e-mails and were
willing to sacrifice the CPU to have them.
I am willing to assist with the development of this feature.
However, I
want to get some ideas and comments from Amavis users and
developers.
Please let me know what you think of this idea.
Thank you,
Cory Visi
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