On the user registration page I would like to ask a few questions to the user to make sure they are human. Obviously I would make these challenging questions which the bots will not know. I am not really bothered about randomising the questions as I will change them ever month or as required. I know a bit on PHP and MySQL so really I just need pointing in the right direction with a few suggestions.
Please do not recommend captcha images as we all know they no longer work, and are extremely annoying. There are bots which can read Google, Hotmail, reCaptcha, VBulletin, PHPbb, and InvisionBoard captcha images which just proves they are not very useful.
I've had a look through the plugin store to see if such a plugin does exist but I can't see one. It maybe possible there is one but it is listed in German.