ok sure, but how many permutations of different questions are there? Once you have these, it is trivial to OCR the numbers/shapes and pick the appropriate one per the question.
Infinite! Just this of the possibilities with that kind of system. You could keep adding different questions (just minor variations) and it won't be difficult to keep ahead of spammers. Plus there is always a trade off between security and ease of use. I think the ease of use with clickcha is well worth the slight loss of security.
I'll give them two guesses who will win most of the time.