Not quite a CAPTCHA, but something similar has actually been done before. The ESP game[1] paired two random people looking at the same image while a timer ticked down. The players had to enter labels that described the…
Something similar exists: iabackup[1][2]. It is designed to host an independent copy of (some of) the Internet Archive using git-annex. You tell it how much storage you want to donate and git-annex fills your disk with…
You're probably thinking of the OFFSystem (https://en.wikipedia.org/wiki/OFFSystem)
Not quite a CAPTCHA, but something similar has actually been done before. The ESP game[1] paired two random people looking at the same image while a timer ticked down. The players had to enter labels that described the…
Something similar exists: iabackup[1][2]. It is designed to host an independent copy of (some of) the Internet Archive using git-annex. You tell it how much storage you want to donate and git-annex fills your disk with…
You're probably thinking of the OFFSystem (https://en.wikipedia.org/wiki/OFFSystem)