On Sep 19, 2005, at 6:36 AM, Stephen Veit wrote:
> I have seen the case where a subscriber is asked to solve a simple
> math problem. E.g., "what is twelve plus twenty-three?" This would
> certainly be accessible. You could think of different types of
> questions like "Enter the number that follows fifty-five." or "What
> number comes before thirty-two?"

Interesting. That would probably keep out existing general-purpose  
rakes. But the moment your site becomes popular or targeted, it seems  
to me that it would not be difficult to write a program to answer  
your questions. Even if you include 33 flavors of how to phrase the  
question ("Enter an integer that is not less than (not equal to)  
eighty (reduced by the value represented by the roman numeral V) and  
more 'n seventy with the number of non-thumbs on a standard hand  
added to it.") the engineered bot could be written to handle 20% of  
your phrases, and that would be enough.

[OT]
I smell a couple of fun Ruby Quizzes here. One is simply to write an  
english-to-numeric processor.
value = Numeric.from_english( "eight-hundred thousand, twenty-three  
hundred fifteen")

Another quiz might be to write such a challenge/response captcha  
system. Make the questions as clear and varied as possible.

Another might be, given a series of questions like the above, to  
write a 'bot that could answer them.