"I'm not a robot" on websites--why?

[Jeffhs]

Why does just about every website which asks for personal information have something called "reCAPTCHA" in a small box? The text near the checkbox says "I'm not a robot", which I find very insulting. Of course I am not a robot (nor are any other human beings who use these sites), so why on earth does this reCAPTCHA box even exist? As I said, I find this extremely insulting and demeaning. Are logins to websites by actual robots that much of a problem that these sites must ask if the person entering information on them are in fact humans, not robots?