Captcha stands for Completely Automated Public Turingtest to tell Computers and Humans Apart, and was first developed at Carnegie Mellon university in 2000.
Second, newer approaches to CAPTCHA have been developed that try a different approach to a Turingtest by asking users to perform operations through input devices, like a keyboard or mouse.
It became clear to me in the early 1990s when for a couple of years I was a judge in the annual Loebner Prize Competition, an annual contest to find out if any computer could yet pass what is known as the Turingtest: if it could fool a person into thinking it was a human.