classiccmp list (sort of) help requested

Listowners perogative to ask a question that is only halfway on topic.... ;) I figure some people here may have some good suggestions - offlist please. There is a SpamAssassin machine(s) filtering spam being sent to the list that sits in front of the classiccmp server (we're also making use of Pyzor, Razor, milter-ahead, and clamav). It's been doing a wonderful job, such that most spam is kept out of the moderators faces. However, over the past few months I've noticed that more and more is getting through (not to the list, but to the moderators eyes who have to kill it all manually). Same goes for many of my customers. What concerns me is that 99% of the new spam making it through is vaguely sensible english phrases (apparently automatically pulled from online books, or from usenet post archives, etc.). If there was also an advertisement text, Spamassassin could catch that. However, the text is all just english phrases (I've noted them to be targeted phrases, like having to do with computers, sometimes old ones) BUT... the advertisement is a graphic attachment. Since SpamAssassin can't do OCR on the small gif or jpg attachment that says "buy viagra here"... I am not sure what to do about this. It comes from all over, not just a few servers, etc. Before you say "just kill all emails with graphic attachments"... keep in mind that these spamassassin machines do their job for thousands of domains that I host, not just classiccmp.org. So just killing all emails with graphic attachments is simply not an option. If anyone can give me a few ideas that will work well for ISP/hosting-class environments, I'd love to hear it. Off-list please! Thanks in advance for any advice. Best regards, Jay West