I'm trying to come up with a good enough anti-spamming mechanism to prevent automatically generated input. I've read that techniques like captcha, 1+1=? stuff work well, but they also present an extra step impeding the free quick use of the application. (I'm not looking for anything like that please).

I've tried setting some hidden fields in all of my forms, with display: none; However, I'm almost certain a robot (which is essentially a program) can be configured to trace that form field id and simply not fill it.

Do you implement/know of a good anti automatic-form-filling-robots method? Is there something that can be done seamlessly with HTML AND/OR server side processing, and be (almost) foolproof? (and please no JS, one could simply disable it, and there goes my anti-spam method).

Btw I'm trying not to rely on sessions for this (like, counting how many times a button is clicked to prevent overloads).