Spam Prevention Techniques (ideas)

So I've been thinking of various spam prevention techniques, from stats & NN to NLP, but, how would you all feel about textual challenge questions?

Either questions I can make up in my spare time about programming (i.e., "Lisp is a ____-level language."), or textual captchas? So you could still post through links or whatever, and nothing would ever leave my server, but it would make it a lot harder to automate posting.

>>4
It can be a random textcaptcha like:
Tell me the [u]N[/u]th vowel on following sentence:

Eat SICP and Dine.

Tell me the one that does not match:

SICP,Ruby,Papa,Haskell,APL

Tell me which is a RL programmer

Kikuri,Shinki,Reimu,Marisa,Sussman,Rika

>>8
Nah no bans on captcha failure. You could implement that after 10 times, they will have to wait a random time of 5-10 minutes, but I advocate against it. Maybe ban ECHELON servers if you can.

Also, you are not thinking of people whole are forced to use the same proxy as other shitposters.

>>9
No idea.