Every step we take to make it harder / more time consuming for the spammers to register, would make it equally harder / more time consuming for the genuine visitors.
b0b gets around it by charging a $5 fee for forum registration. One thing spammers won't do is part with their (not-so-)hard-earned cash!
Other forums opt for the admin to validate registrations, rather than use first post approval. This actually creates more work for the admins, as every single registration has to be checked manually, rather than just dealing with those who go ahead and post, as only a fraction go as far as posting. For example there were 20 spam registrations yesterday, but only 3 posted. It's far easier to deal with the 3 who post than manually vet the 20 registrations, and since the first posts are moderated nobody except the admins see them, anyway, before they are deleted.
The registration form uses a
CAPTCHA which is now owned and ran by Google (
reCPATCHA). The spammers are usually not humans but automated "bot" scripts which trawl the web looking for forums to sign up to and submit their rubbish to. But, there can be humans behind these solving the CAPTCHA part for a very low wage.
Recently there has been an increase (not just here) in spammers either solving the CAPTCHA or successfully circumventing it. There are millions of websites using ReCAPTCHA and the advantage of a centralised system is that if it is compromised this is evident early on and steps can (and will, I'm sure) be taken by Google to close the gaps. With spammers it's always an ongoing battle, though.
