Or “telling humans and computers apart (automatically)”. This was a new one on me. I’m familiar with tricks to avoid automated abuse of services such as displaying obfuscated images of text that the user must then type. I hadn’t seen it refered to as CAPTCHA before.
For the curious CAPTCHA stands for “Completely Automated Public Turing tests to tell Computers and Humans Apart”.
Here’s an example:
The CAPTCHA Project at Carnegie Mellon has lots more on this.
Eddies in the Space-Time Continuum 
jjmahe
/ August 6, 2004Very nice CAPTCHA ! and thanks for the translation of the acronym.
Calum Benson
/ August 6, 2004A bit crap if you’re blind though..,.
Chandan
/ August 6, 2004A text based Turing test would be to just give simple riddles that you cant search on a search engine to find the answer, and should be easy enough for humans to guess the answer. So my email address might be
chandan at “we make the net work” dot C0M
or chandan (a) “(not moon) D0t CoM”.
Then it can’t be “Completely Automated…” 🙂