How can I get a box on my website that maintains automated programs to register?

How can I get one of thoose boxes with letters and numbers in the place where you type the right letter / number to submit something? They prevent automated programs from creating accounts and sending spam. If you can tell me what do you call it would be great! Here is an example of one them: https: / / signup.live.com / signup.aspx? ru = http% 3a% 2f% 2f% 2fmail.live.com% 3frru 3dinbox% & wa = wsignin1.0 & rpsnv = 10 & ct = 1238712894 & rver = 5.5 .4177.0 & wp = MBI & wreply = http:% 2F% 2Fmail.live.com% 2fdefault.aspx & lc = 1033 & id = 64855 & mkt = Fr-FR & bk = 1238712895 & rollrs = 12 & lic = 1 box at the very end of registration.

It is called a captcha "and is a picture to avoid spam and / or other electronic recording system. You can create your own http://www.captcha.net/ or you can use EMailMeForm http://emailmeform.com/ to create an entire form with a database automatically. Hope this helps!

[affmage source="ebay" results="100"]Automated Website[/affmage]