CAPTCHA, the short form of Completely Automated Public Turing test to tell Computers and Humans Apart is essentially a sort of test that recognizes whether the user is a computer or a human being. It comes under the trademark of Carnegie Mellon University. For more information, you can go to http://www.protectwebform.com/.
When you take the test that CAPTCHA gives you and give the right answer, it knows that you are a human. For instance, it will ask you to key in letters from a distorted image of alphabets and numbers. The machine will not be able to figure it out correctly. That makes it quite easy for CAPTCHA to know the difference. You can get further details from http://www.protectwebform.com/smartcaptcha.
If you've put your email address anywhere on your website, there's no doubt you've gotten a lot of spam because of it. Unfortunately what you do to let those who visit your website contact you, is what bots (animated programs searching the web for user id's and emails) are looking for. They grab a hold of that email address and add it to their lists that are about to be used, without your permission, for spamming.
Another option is CAPTCHA that does not allow the spammers to get access to your email ids. Many websites and sign-up pages use CAPTHCA. It assumes that computer programs cannot read distorted characters. It is considered fairly reliable.
As a fully automated program, CAPTCHA is so advanced it creates tests that can only be completed properly by humans. And since it runs itself, you don't have to baby-sit the system for it to work. This is why so many webmasters use CAPTCHA to keep their sites safe and secure.
Spammers are a nuisance. Once they get hold of your email id, you are bombarded with spam mails and you can never be sure what your id will be used for. This is where CAPTCHA comes to your rescue by preventing abuse of your system.
Many email services and online blogs are the ones who could benefit most from CAPTCHA. If you have webmail accounts through Gmail, Hotmail, or Yahoo, you know how many spam e-mails seem to get into the system. In addition if you regularly read online blogs, you have likely seen some that have had a long string of spam postings. CAPTCHA can stop these posts from happening by catching the spamming programs before they have a chance to do their work.
Attempts to make CAPTCHA handier, like the use of JavaScript, mathematical questions or simple questions requiring common sense answers have failed because either they cannot be automatically created or they can be easily split given the condition of false intelligence. So, the only security these CAPTCHAs provide is safety through obscurity.
