Cartpauj Register Captcha does one simple task, and does it well. It adds an extra CAPTCHA field to the registration form in WordPress.
2. Activate the plugin through the ‘Plugins’ menu in WordPress.
3. Done! If you’d like to also replace the default WordPress logo on the login/register forms please see the note at the bottom of the “cartpauj-register-captcha.php” file for a how to.
== Note ==
Cartpauj Register Captcha should work with older versions of WordPress as well but was not tested with anything older than 3.0