Google’s recaptcha is used to help train image-recognition programs (like all those ones having you identify signs/bicycles/stoplights help Google’s self-driving cars)
They used to have the 2 words, where one word was the control and one word was from a physical book that Google was trying to digitalize

At this point, I think they have less than 24 hours of air left, so I highly doubt they’ll be alive when/if the sub is found