It's funny you mention this - right after I read a whole thread about this issue in another Linux mailing list.
I haven't tried this, but people recommended the following: http://wiki.apache.org/spamassassin/FuzzyOcrPlugin
In continuation to this - I've just saw a positive report about installation of Maia, a web-based interface to this whole SpamAssassin+Amavis setup.
http://www.renaissoft.com/maia/
Cheers,
--Amos
