Unfortunately adding questions, captcha's, images or combination of questions and images like the one you showed Adam will only be circumvented by spammers who use bots that request human interaction if they can't get past the the signup page, that's assuming the signup is done via bots and not by an Chinese spammers who have 100's or 1000's of people signing up to forums, once signup is confimed the system adds it to the spam list and the bot then logs in and does it's thing.
For every step taken by admins to try stop spammers, there will be a way to get around it and the 'hardcore' spammers have already automated systems dedicated to get around these antispam measures, some of which I've listed above.
The only real way would be to use AI in the forum software watching every post looking for tell-tales signs of spam and blocking it before it's written to the DB