Random image text generation?

[Leif K-Brooks]

Steven D'Aprano wrote:
> For a text only solution, consider putting up a natural language question
> such as:
> 
> What is the third letter of 'national'?
> What is four plus two?
> How many eggs in a dozen?
> Fill in the blank: Mary had a little ____ its fleece was white as snow.
> Cat, Dog, Apple, Bird. One of those words is a fruit. Which one?

That wouldn't work as a true CAPTCHA (Completely Automated *Public* 
Turing test to tell Computers and Humans Apart), since making the list 
of questions and answers public would defeat its purpose.