CAPTCHAs don't always work to keep bots out, anymore.
For one thing, people are hired to solve them...I think many of the services are based out of Manila. There are also bots that work off of a dummy site, where naive users solve a re-directed CAPTCHA and the dummy site gives them access to some cheap content. It would probably help somewhat, though.
I'll keep reporting stuff.
I've suggested this before, but might a Bayesian filter help? A lot of the spam I see is focused on just a few topics, and presumably you have a good corpus of spam and not-spam to train such a filter with.
"the qualities of these bacteria, like the heat of the sun, electricity, or the qualities of metals, are part of the storehouse of knowledge of all men. They are manifestations of the laws of nature, free to all men and reserved exclusively to none." SCOTUS, Funk Bros. Seed Co. v. Kale Inoculant Co.
This is awkward. I've grown a second evil head. I'm going to need a machete and a tiny ad ...
Devious Experiments for a Truly Passive Greenhouse!