^^
1. You Have to Set "KeyCAPTCHA" on the "Options" > "Human Verification", and Save that Setting.
2. It replaces the Image Verification Code so if Image Verification Works on Your Web Site KEYCAPTCHA Should Work Too because it Replaces the Code of the Image Verification on all the Places were it Works.
3. Also on "Options" > "KeyCAPTCHA Settings", You Should Write the "Private key" and the "KeyCAPTCHA code", and Save those Settings. (On the KeyCaptcha Web Site You Should Set the Code to Work on "vBulletin" Board).
4. The KeyCAPTCHA Team are Really Nice and Polite People (Read all their Replies), so Ask Them Nicely For Help (and Create a Ticket on their Web Site), and They'll For Sure Assist You and Help You To Solve the Reason Why the Code isn't Displaying in Your Web Site. But Ask Them Nicely, KEYCAPTCHA is a Very Good Product and Offer a Great and Useful Service.
5. The KeyCAPTCHA Team Will Help You With The Rest, They're The Experts.
My Best Regards.