I thought we had it on if you mean the random letters and numbers people had to copy when they registered, but I'll check with my webmaster. How does having it on or off make a difference?

I didn't understand what do you mean in full, but if you mean Captcha, it's an optional feature to miniBB. The software could be configured to be protected even without it; but this module slightly make the life easier, because it stops automated spam which comes from other programs and robots; they can't recognize it and substitute these numbers easily, and that solves the "human detection" problem, because on forums you mostly want all users to be humans, right? ;-)