To cope up with the social trend, this site opened up its user registration after almost seven years of being online. It is a fact that spam registration is inevitable once it is opened. The plugin WP-recaptcha worked flawlessly without any issues at all.
Then the next step of the transition to cope with the social trend was to integrate BuddyPress as an alternative to article comments. This move was also to initial discussions among site visitors. Unknowingly, the user registration proces was taken over by BuddyPress. This made the WP-recaptcha useless as its integration hooks are designed for the WordPress core functions. Other WordPress recpatcha plugins were tested but to no success. Then after some analysis, BuddyPress Captcha was installed. After completing its configurations, it was tested successful.
BuddyPress forum keymasters, stop spam registration on your blog / forum sites, use BuddyPress Captcha instead of a purist WordPress Captcha.