How do i get rid of spam and advert bots registering?

[Neo_Angelo]

I'm having a big problem over at my boards, i swear i have several spam and advert bots keep registering on my forums (using names like Adultlink, UScredit and stuff) most of the Emails are really weird and end in .ru or .de or stupid E-mails.

i've tried everything to block them from registering, from Admin validation to making new registrations unable to post, to banning the IP's and they STILL return! i've even shut off new registrations for a time being hoping that if it was a human they'd give up but to no avail.

i hate things like this as my forums have now become fort Knox in which is ridiculous as i have to spend a good 10 minuites or more ach day deleting fake and crappy accounts.

how are they getting through user image veryfication and how do i stop them altogther, i've even banned Emails and blocked usernames like Adult and Credit.

Any help would be appreciated.