This plugin add a simple math captcha to comment form.no javascript,no css included,just some php code.should just stop robot spammers.
just add all php codes to your theme’s function.php will do the work too.visit
http://html5beta.com/wordpress/wp-simple-captcha/
for more info.
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.