SI CAPTCHA Anti-Spam
http://wordpress.org/extend/plugins/si-captcha-for-wordpress/
Today I updated it for latest version of buddypress 1.2.3 compatibility
This plugin adds CAPTCHA anti-spam methods to WordPress on the comment form, registration form, login, or all. In order to post comments or register, users will have to type in the code shown on the image. This prevents spam from automated bots. Adds security. Works great with Akismet. Also is fully WP, WPMU, and BuddyPress compatible.
