MyBB Community Forums

New user is getting an error message saying something about invalid image verification code

That means you dont have your captcha set up correctly. Check the templates in updated templates.

You can learn more about AntySpam measures here: http://en.wikipedia.org/wiki/CAPTCHA

I recommend geeks plugin.

http://mods.mybb.com/view/registration-s...y-question

This allows you to add your own custom questions