Jonathan Fleury

This is a “draggable” captcha. Images have to be dragged into ascending order.
IMPORTANT : This pluggin require PHP 5.4 and GD extension.

Guroot Captcha

This is a "draggable" captcha. Images have to be dragged into ascending order.

Todd Nestor

Hercules Recaptcha uses the latest Google Recaptcha API to more accurately determine if users are bots or not. 
If the user is not logged in it will display a Recaptcha for the user to fill out in the comment form. If the user 
disables javascript and is not logged in then comments will fail to submit.
The Recaptcha is also added to the registration page for both multisite setups and single blogs. There are options for 
having it show up on comments and/or the registration page, as well as options for its position on the comment form, and 
which style (Google gives only two options, dark or light).

Hercules Recaptcha

Hercules Recaptcha adds a Recaptcha to the comment form for non-logged in users.  It uses the latest Recaptcha API.

Guroot Captcha vs Hercules Recaptcha