Absolutely spam proof form

[temi]

I have been bombarded with spam from my sites via the contact forms recently, the spammers seem to have cracked the image verification code too, does anyone know and absolutely spammer proof way to implement a form on my site?

 

[PrivateInvestigator]

I've now switched to having only one form (as opposed to one form on every page) due to the same problem.

I couldn't find one that makes visitors input numbers etc but I did have one that shows IPs for easy banning.

 

[temi]

Thanks for that PI, IP banning is not a good solution as most of they and on dial up IP and they get allocated another IP next time they dial up sto spam you