Are there open source CAPTCHA solutions available?

Question

I'm in the process of adding CAPTCHA validation to one of my websites and need to know what open source solutions exist. Please note strengths and weaknesses and what platform they work with. I'm primarily interested in ASP.NET solutions but feel free to include PHP, Java, etc.

Answer 1

ReCAPTCHA is the same one StackOverflow uses. It has an ASP.NET implementation.

It uses a webservice to provide the captcha images; this is an university trying to digitize difficult to OCR texts. I'm not sure how easy it would be to replace this portion. There are many open source client implementations, as the API is quite well documented.

Answer 2

Have you taken a look at ReCAPTCHA?

Answer 3

Jeff Atwood has a captcha control + source hosted on his coding horror site

ReCaptcha might be another alternative but i don't think the source is open.

Answer 4

Have you seen JCaptcha? Not an ASP framework, but might be useful.

Answer 5

Try this one... http://www.codeproject.com/aspnet/CaptchaImage.asp very nice article!

Answer 6

In the Java world, check out jcaptcha.sourceforget.net

Answer 7

One I just found but have not tried out is MyCaptcha

Answer 8

ReCaptcha has many benefits. The fact that google owns it is a big plus. We used to use ReCaptcha on my project, but the firewall in our production environment cannot handle add entries based on domain name, only based on IP addresses. ReCaptcha has switched to using Googles infrastructure, so the IP addresses are no longer publicly available. Our production environment is locked down extremely tightly, so there are no workarounds possible -- we have to start using a new captcha. If you're in my boat, ReCaptcha won't work for you.

Answer 9

Confident CAPTCHA is a free solution that is much less irritating for your website visitors than those hard to read CAPTCHAs. Instead of making your visitors decipher warped text, it simply asks them to click on pictures. You can see how it works here: http://demo.confidenttechnologies.com/captcha/

Easy to use PHP libraries are available currently, with ASP.Net libraries coming in the next week or so. Plugins for Wordpress, Joomla and Drupal also coming in the next week.