Free Open Source CAPTCHA Script

CAPTCHA (acronym for "Completely Automatic Public Turing test to tell Computers and Humans Apart") is the most common and effective spam protection technique. CAPTCHA is a type of challenge-response test used in computing to ensure that the response is not generated by a computer. While the computer can generate the CAPTCH it can not solve it. So any user entering a correct solution is presumed to be human. A common type of CAPTCHA requires that the user type the letters or digits of a distorted image that appears on the screen.

Protect your form, guestbook, forum, blog etc. from spammers with these free CAPTCHA scripts.

Phoca Captcha
	Phoca CAPTCHA class is a small free class to show CAPTCHA image in your form. You can safe your form from Spam. You need PHP with GD library but you need not TTF support. Requirements: PHP 4.4.1 (or any later version) with GD library (graphics library for thumbnails... [ Detail ]

KCAPTCHA
	KCAPTCHA is a free and open source PHP solution to generate human validation images (CAPTCHA). KCAPTCHA is meant to be a very strong protected one but requires no special hosting features, only PHP with GD library. How it works Script creates session and writes to it with name... [ Detail ]

HKCaptcha
	This one is written with the current state of captcha-defeating research (as of 2007) in mind. Apart from a mathematical letter distortion algorithm that is more than just rotating the letters, the clutter is designed to make segmentation of the image into separate letter glyphs hard to do automatically.... [ Detail ]