system
A chat on subreddit /r/NoStupidQuestions
human
It'll happen a little anyway, but if you're using a VPN or something along those lines it'll happen a lot more often. 

It's there to stop written programs (bots) using things like Google, or signing up on services and sending spam messages or whatever other endless possibilities of automated mischief. 

The idea is that a written program won't know how to interpret the request of the "prove I'm human" tests and thus will fail the test.
gpt
Thanks this is really helpful. I think VPN may be the culprit for the uptick.