Ordinary captcha useless
It has been for months. I run a forum and about six moths ago I started getting a constant stream of bots signing up _and activating the accounts (confirmation email)_despite the captcha. I looked around for a solution and found a simple one: include a simple random question in the registration form, something like "Are you a human?" or "How many toes do you have?" - something obvious to a person but enough to stump a bot. Ever since I did that I'm bot-free.