AjaxLine

Great commercial solution

TheCAPTCHA

TheCAPTCHA — a powerful php script to protect your site against spambots. TheCAPTCHA is free, you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License.

Supported technology: PHP.

Securimage

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. Securimage does everything from generate complicated CAPTCHA images to making sure the code the user entered was correct.

Supported technology: PHP.

ReCAPTCHA

reCAPTCHA is a free CAPTCHA service that helps to digitize books, newspapers and old time radio shows.

Supported technology: PHP.

JCaptcha

JCAPTCHA stands for Java Completely Automated Public Test to tell Computers and Humans Apart. The open source java framework for captcha definition and integration.

Supported technology: Java.

3DCaptcha

3DCaptcha is the "captcha nice to humans, bad to machines". It is written in PHP and features a new approach to captchas, using human's spatial cognition abilities to differentiate humans from machines.

Supported technology: PHP.

ProtectWebForm.com

Free and useful service providing CAPTCHA smap protection for your blogs and forums.

Supported technology: PHP.

Free CAPTCHA-Service

This server provides CAPTCHA images and audio files you can use in html-forms. CAPTCHA images can prevent forms to be used by robots. It supports various server technologies.

Supported technology: Multi-Platform - PHP, ASP, Python, Perl, Ruby, JSP.

VidoopCAPTCHA

VidoopCAPTCHA is an image-based verification solution used to distinguish a human from a computer program, protecting web sites against malicious bot attacks. When compared to traditional text-based CAPTCHAs predominant on the web, VidoopCAPTCHA is easier on the user.

Supported technology: Multi-platform - PHP, Python, Ruby, .NET.

IronClad Captcha

Professional and free CAPTCHA service for your sites.

Supported technology: PHP.

ASIRRA

Asirra is a human interactive proof that asks users to identify photos of cats and dogs.

Supported technology: JavaScript.

Great commercial solution -BotDetect ASP.NET CAPTCHA

Back in 2004, BotDetect CAPTCHA was the first commercially available captcha software on the market. Four years and more than fifteen hundred paying customers later -- Lanapsoft is by far the biggest fish in the commercial captcha software pond.

It is mature and enterprise-ready captcha product that unlike majority of other captchas:

• supports audio in all major web browsers (IE, FF, Safari, Chrome & Opera),
• validates properly when pages with captcha are simultaneously open in multiple tabs,
• produces XHTML 1.1 Strict and WCAG AAA compliant semantic markup,
• is ASP.NET Ajax and ASP.NET MVC compatible,
• works with ASP.NET control frameworks from Telerik and other vendors,
• is easy to integrate into SharePoint sites.

To make it easy for humans, BotDetect CAPTCHA team is focused on readability of individual captcha algorithms. At the same time, random use of 50 of those algorithms is what makes life a misery for captcha-breaking software writers.

Great commercial solution - ASP Captcha

This is a captcha than can be inserted directly from the Dreamweaver menu. No hand-coding required, it's a 100% visual process. This captcha works entirely in your web server (no external services required) and it doesn't require external components or additional installations since it has been built with 100% classic ASP code. The form fields are re-filled automatically if the user types a wrong code.

Supported technology: ASP (similar products available for PHP and Perl)

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