how to enable captcha and verification question
-login to smf with the admin account then goto Administration > Configuration > Security and moderation
-under "Anti-Spam Verification" section enable: Require verification on registration page .
Also set Post count under which users must pass verification to make a post pick a number that is not too high I will recommend "5".
-next move to "Configure Verification Methods" section and enable both methods (image and question).
- move to " Verification Questions" section and set questions and number of questions you want users to answer. Ask simple questions and set answers that are not case sensitive. An example of a good question is: how many colors are in the Nigerian flag? (which the obvious answer is 2).
that's all if you have any question use the comment box (quick reply)