The Other Side of CAPTCHA [closed]

CAPTCHA stands for "Completely Automated Public Turing Test to Tell Computers and Humans Apart", but we only consider one half of it i.e. a test to separate genuine humans from bots.

Can a program/test exist that can be only "solved" by computers/bots and not by humans?

If not, what prevents such a program from existing in the foreseeable future?

If it does, could you please cite it and how it works?

Note: The Voight-Kampff Test by Phillip K Dick still has its drawbacks.