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.
Website owners have to guard against spammers yet they need feedback from the visitors to their site. Spammers are always on the look out to grab your email id and use it for various purposes without your permission. One option is that you can go in for automated programs, called bots, to let them scan your website and parse out your mail id.
If you want to keep bots from getting your information, consider a CAPTCHA. Once you put the CAPTCHA online, as someone wants to sign up to get access to your information they will have to type in the letters that are being shown in a distorted image (i.e. http://www.protectwebform.com/plugin_wordpress). If they can't, CAPTCHA knows they are a computer and will turn them away.
CAPTCHA has become very popular in the past few years because it is a program that can create tests which only humans can clear. Since the program is fully automated there is virtually no chance of any human intervention. No wonder, most website owners go for it.
The key to CAPTCHA is using it to stop spammers before they ever get access to your email. Once they have it, you have lost the game and they will be regularly sending you spam emails you don't want.
In other words, CAPTCHA not only prevents encroachment by spammers for commercial purpose, it also protects the systems that are gullible to spam like, the webmail services of Gmail, Hotmail, and Yahoo. They also help prevent automated postings on online blogs. CAPTCHA helps in enforcing a usage policy and prevents any kind of deviation from the policy. This is required in case a service allows automated use but within a limit.
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.
