Interesting stance. I have bought many tens of thousand of captcha soves for legitimate reasons, and I have now completely lost faith in them

That's actually a good idea. A very simple "click the frog" captcha might be solvable by an AI but it would work as a way to make it more expensive for crawlers without wasting compute resources (energy!) on the user or slowing down old devices to a crawl. So in some ways it could be a better alternative to Anubis.

Originally called hashcash: http://hashcash.org/