Back in darker days of the internet, image spam was a huge problem. At that time I found a fix that solved the problem for myself and my hosting clients. I posted the following to my blog:
[Updated 1-sep-2013: correct the link to the image spam article]
This absolutely rocks. No more bloody share trader and stock dumper spams.
The trick is to use optical character recognition to convert the images in the spam to text. Spamassassin is then able to read the text and process the email just as it would any other text spam email.
Anyway check out GIF Spam — Setting up the ‘OCR scanner and image validator SA-plugin’. The only thing you’ve got to lose is some very irritating emails.