What are ways to verify new members on a website?

I am starting a service on a website. I don't want it to be over ran by spam and scams so I want each user to be verified. I know nothing won't completey take it away but it will at least cut down on the number. I know there is the phone verification service is there another way or other ways that a user can be verified? Please help any ideas. Thank you

 

http://recaptcha.net/ might help you. I've no experience of phone verification, but flippa.com use it on their site if that's any help.

 

you can use live chat.............to track your visitors if they are new or returning visitors.....

 

If your using any type of forum StopForumSpam is a great site check it out