We actually implemented a sort of a poor man's Turing test on a website that allowed anonymous submissions. Not unlike an imageboard's reply function in fact.

It goes like this: In addition to the name/link/content fields in the form, you stick a text field in there with the label "leave this field empty". If the field is not left empty, silently discard the posted data. Since spambots tend to fill every field in with spammy garbage with little discrimination, they would fall for the test. No Javascript and no captcha involved, compatible with blind people.

There's quite a few variations and improvements upon this theme that you can come up with too.