Multiple CAPTCHA Engine is a system plugin to produce and verify captcha images.
With this new version, you will get 4 different captcha systems (libraries):
1. SecurImage PHP library (requires GD image Library),
2. ReCAPTCHA (requires an API key from recaptcha.net);
3. MathGuard, simple but effective.
4. VouchSafe, a New Spam prevention approach. (only compatible with Contact Enhanced and iRecommend)
 - http://ideal.fok.com.br/joomla-extensions/component-contact-enhanced.html
 - http://ideal.fok.com.br/joomla-extensions/module-ajax-recommend.html
 - http://ideal.fok.com.br/joomla-extensions/module-ajax-contact.html
 - http://ideal.fok.com.br/joomla-extensions/component-irecommend.html
This plugin does work with Joomla! 2.5, however it only works with selected extensions.
I'm sorry about the inconvenience.
The reCaptcha code works fine, but there is no support for multi-language and the support for handling the 'error=' parameter on the reCaptcha API which allows reCaptcha to show the user errors directly is not complete. I had to modify the plugin to get these parts to work.