Image v Question
> At a web site that I help manage, image-based CAPTCHA was recently implemented
> to replace text-based CAPTCHA which had been cracked by spam bots for a long time.
I used to get about 5 porn-spam-bots a day on my phpBB forums once they had figured out the built in image CAPTCHA system. I switched to a simple question based system which asks a random question like "What colour is the sky?" and I've not had one bot sign up for the last two years. Sure, it's not a multi-lingual system but if that's not a problem for you it really seems to work.