reCAPTCHA

[Jeko]

http://recaptcha.net/learnmore.html

If you have a website, you can use this service...
I'll use it in my sites!

Read the link to learn more... There is also a service to post email in forums with security from spammers.

[Zacariaz]

This is really a nice idea, however the quality leaves something to be desired and also I'm not certain there is any kind of error checking, even when I write something incorrectly on purpose it tells me that it's correct.

[Jeko]

This is really a nice idea, however the quality leaves something to be desired and also I'm not certain there is any kind of error checking, even when I write something incorrectly on purpose it tells me that it's correct.

Yes, there is error checking, read all this page: http://recaptcha.net/learnmore.html

[Zacariaz]

Okay, that explains it. Seems like a solid system.