I finally found something to filter out that damn image based spam!
Simple message filter rules:
http://www.imarc.net/blog/102/how_to_filter_imagebased_spam/

I got it set up in Thunderbird.

The ones I've been getting lately are the randomized subject with a random name as the sender.

I've had a bucketload of these over the last month and I've otherwise been spam free for years. I've even been receiving automatic returns to junk mail sent from an address similar to mine. I'm not sure my ISP has got that one right.

That's why filtering on the content-type will help. Although I do have every now and then to add an address to my address book of a mailing lists that use that content header.

I'm getting another type now that has weird, munged looking URLs and it gets past my filters.