A coworker came across the following CAPTCHA. Finally, one that can beat spammers and their bots!
PingBack from http://www.easycoded.com/a-captcha-that-beats-bots-and-spammers/
Quite funny but a light went on...
So I thought how about a captcha for a captcha? The main captcha would be a bit like the above example in the way that it has multiple colors/styles of characters (though a bit less so ;). Then there would be a second dynamicly generated png/gif/etc... that would tell the viewer to enter the red letters only.
Of course there are other issues (like color blindness) so perhaps the choices would have to be bold/dashed/dotted/slashed/lined-out/etc...
Is it perfect; of course not. But it would be an order of magnitude tougher for a bot and the original captcha would have to rely less on distortion which would make it easier for humans.
Why not just have an image with the caption "What kind of animal, (car), (etc) is this?"
Hey Terry, attribution where it's due: http://ars.userfriendly.org/cartoons/?id=20081005
Actually MSR has something similar to that: