A Captcha that is accessibility friendly?

I hate captcha's full stop but i am thinking about implementing one on each of my directories after my Apex URLs directory gets roughly 1000 spam bot submissions per day in the form of categories/link/comment submissions.

However i want to foil the bots whilst not hindering accessibility, is there a solution?

 

I've seen some that will speak the word. I'm not too fond of those tho.

The ones I like the best are where they simply ask a question like:

What is 2 + 4?

Or is fire hot or cold?

G-Man

 

hmmm, those questions seem pretty effective

 

2+4...
Thats too simple, one of my directories asks for the integral from -1 to 1 of 1dx...

 

Do you know of a source where i could learn how to make such a feature or maybe where i can find it?

 

Should only take some basic html with javascript or html with php... make a form box, then check it with an if statement... if the answer is not right dont go through.

 

ye, I would add that, but what you should put is some things and a rotator, so that it sometimes show 2+4, others 3+6, others 1+1 and so