What is CAPTCHA?

The term CAPTCHA, based upon the word Capture, is a type of challenge-response test used in computing to ensure that the response is not generated by a bot. The process usually involves one computer asking a user to complete a simple test.

Using a CAPTCHA Script on a website is a great way to ensure that response is made by a real person and not by a spambot and it helps prevent automated abuse of your site such as comment spam.

There are many CAPTCHA scripts available, lets dig into the list together.

Image Based CAPTCHA

Fresh & Creative Alternate to Traditional CAPTCHA Scripts – slideLock

slideLock adds a jQuery UI slider along with labels and notes. The user simply slides the form to unlock the submit button and then both client side and server side validation techniques ensure secure submission of the form.

reCaptcha

Stop spam and help digitize books at the same time! The words shown come directly from old books that are being digitized.

Photo CAPTCHA System – identiPIC

identiPIC is a photo CAPTCHA system whereby a website visitor has to identify a picture to proceed. The system is typically used on web forms to block spambots.

s3Capcha jQuery Plugin

A lightweight CAPTCHA jQuery plugin which works with a simple click.

Ajax Fancy Captcha

Ajax Fancy Captcha is a jQuery plugin that helps you protect your web pages from spammers. If offers an intuitive way of completing “verify humanity” tasks. In order to do that you are asked to drag and drop specified item into a circle.

Clickcha – The One Click CAPTCHA

Clickcha is a unique CAPTCHA system that more secure than traditional text based CAPTCHAs yet easier to use. Clickcha is currently available as plugin for WordPress and bbPress. It can also be integrated into any CMS using the simple Clickcha API.

MooTools Bot Filtering CAPTCHA Class

Don’t read, just drag the right option into the block hole.

Open Source PHP CAPTCHA Script

Securimage is an open source free PHP CAPTCHA script for generating complex images and CAPTCHA codes to protect forms from spam and abuse. It can be easily added into existing forms on your website to provide protection from spam bots. It can run on most any webserver as long as you have PHP installed, and GD support within PHP.

Image Based CAPTCHA

It uses a distorted point for human verification. It is easy to notice a slightly distorted point over an image. Its obviously a good option to click once instead of typing 5-6 letters. Look at the demo for better understanding.

Flash Based CAPTCHA Script – Internet Captcha

Internet Captcha is a flash based CAPTCHA script for ASP and PHP designed to protect your HTML forms. It comes with a friendly configuration screen to edit interface and security level.

More resources:

• http://captchator.com
• http://www.tipstricks.org – Classic ASP based CAPTCHA
• http://www.spamerator.com – Spamerator can be integrated with any language including PHP, VB, ASP/.NET, Java.
• http://www.captcha.cc – Free service to place very hard CAPTCHA images in front of a form submission.
• http://www.textdisguise.com
• http://rodomontano.altervista.org/engcaptcha.php – Static and animated CAPTCHA script generator.

Text Based CAPTCHA Scripts

textCAPTCHA

Its a web service and comes with a unique API. Whenever you require a logical question, it requests to the server and the server returns an XML response containing a randomly selected question and answer.

PHP Text Captcha

A method of using a question / answer CAPTCHA system for determining whether one is dealing with a human visitor or a naughty robot.

Open Source Javascript Library for Client-Side Validation

LiveValidation is a small open source javascript library for making client-side validation quick, easy, and powerful. The technique used in this Javascript Validation Library can be implemented as a CAPTCHA.

Further readings:

• MathGuard PHP form anti-spam protection – Comes with an expression consisting of two random numbers, one text input field for user’s answer, and one hidden field with the hashcode.
• A better CAPTCHA Control – This Free CAPTCHA control generates numbers and letters which are HTML and not an image.