>      Think creatively.  You could fairly easily come up with a text
> based captcha system that was screen reader friendly and had no external
> dependencies.  For example test riddles / story problems that would be
> dirt simple for a human but next to impossible for a program "in the
> general case" could be rather easily generated in pure ruby.
> 
>     For example:
> 
>           Three things that go "quack" landed in a circular pond
>           that was 10 meters across.  They found fourteen early shoes 
>           and each of them ate as many as he wanted.  How many shoes 
>           were left?
> 
> Most humans could get this on their first try

I disagree; I'd be surprised if more than 10% of the general population
could get past that barrier (although maybe if you gave them two or three
tries you'd get more).

I was listening to a (UK) breakfast radio show this morning, and they
decided to give some questions from a pub quiz. The question "what is two
cubed divided by two squared?" had the *presenters* stumped, let alone the
audience.

Perhaps that duck example is not typical of what you were proposing, but in
any case I find it highly ambiguous. Are we supposed to assume that ducks
don't eat shoes? (=> Answer 14). Or to assume that all the shoes would be
eaten? (=> Answer 0). Since we are clearly in a nonsense world here, with
such things as "early shoes" which don't exist in the real world, we can
apply whatever rules we like to come up with an answer.

Or, given that there were 14 shoes, perhaps 7 were right and 7 were left.
(Argh!!)

Regards,

Brian.