This is a “draggable” captcha. Images have to be dragged into ascending order.
IMPORTANT : This pluggin require PHP 5.4 and GD extension.
Can I change the images used by the captcha ?
Unfortunatly, this will only be available in a future version. If you are comfortable with mysql, you can change them in the wp_GURCAPTCHA_Images table of your wordpress installation.
First version uploaded to WordPress plugin directory.