CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) are of challenge-response test used in computing to ensure that the response is not generated by a computer. Because application are unable to solve the CAPTCHA, anyone providing a correct solution is assumed to be human. A common type of CAPTCHA requires that the user type the combination of letters and digits of a distorted image.
CAPTCHAs is deployed to protect vulnerable systems to e-mail spam. Much of spam is a result of the abuse of free email services. A person can log into a free email account and within minutes can send many unwanted emails to whomever they want. Automated input by software can keep inputing data to your database. This can make your website down.
Resource:
- Captcha creator – http://www.captchacreator.com/
- Captcha script – http://www.puremango.co.uk/cm_php_captcha_script_113.php
