CAPTCHA is dead, your only resort is admin activation or QA.
Unfortunately the former is a headache and the later is an ever escalating Cold War that will inevitably end in Strong AI ruling the internet.
I'm the web admin of a local gaming con's site and forum, and after 9 months of absolutely no bots getting through my QA+CAPTCHA plugins (phpBB) I was bombarded with 1000 bots in 4 days and hundreds of posts about free/cheap prescription drugs/contact lenses and pictures of boobies.
Sometimes I hate the internet...