("CAPTCHA" is an acronym for: Completely Automated Public Turing test to tell Computers and Humans Apart)
CAPTCHA is used to prevent automated software from performing actions which degrade the quality of service of a given system, whether due to abuse or resource expenditure. Although CAPTCHAs are most often deployed as a response to encroachment by commercial interests, the notion that they exist to stop only spammers is mistaken. CAPTCHAs can be deployed to protect systems vulnerable to e-mail spam, such as your e-mail server. CAPTCHAs have also found active use in stopping automated posting to blogs or forums, whether as a result of commercial promotion, or harassment and vandalism. CAPTCHAs also serve an important function in rate limiting, as automated usage of a service might be desirable until such usage is done in excess, and to the detriment of human users. In such a case, a CAPTCHA can enforce automated usage policies as set by the administrator when certain usage metrics exceed a given threshold.
The Goal of our CAPTCHA SCRIPT is to stop spammers, and automated programs or scripts from making post and/or submitting an online form.
There are many free tutorials out there on accomplishing this process, ours sets up in 5 minutes or less, and works on Windows or Linux servers without issue, the ONLY REQUIREMENTS PHP 4+ and the GD Image Library installed, this library is very common on every install of PHP, ABSOLUTELY NO PROGRAMMING KNOWLEDGE NEEDED. So if it needs to work, and work effectively, and time is of the essence, this script is for you.
Our Image Verification uses both letters and numbers against a 1 of 4 included background images, making it nearly impossible for any OCR (Optical Character Recognition) software from reading it.
Our CAPTCHA Code also randomly shifts the position and "tilt" of each of the characters as well as the color of the character.
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The term CAPTCHA was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas J. Hopper (all of Carnegie Mellon University), and John Langford (of IBM), and is trademarked by Carnegie Mellon University