Great stuff Kris. Thanks a lot.
Gonna implement it at the first site tomorrow.
Not expecting to make money with it but for sure every one of those who see this captcha will know what bitcoin is.
How did it work out?
Christmas and New Year got in the way.
The plugin is already installed, but only working on 1 post and it won't be easy to make it work on older posts without editing each one of them, so I'll probably use it only on new posts, which I'll start making again in the next couple days.