How do Captcha and picture codes come to know if the user is a robot?

Answer 1

They don't really. Just yesterday i was trying to pass "I'm not a robot" test. It failed several times with *try again*(i was tapping the squares correctly, took me 5 to 10 mins to get the check mark)
Those codes must have the values of pictures to select stored in it and depending on how many you get right(according to the program) you may not be considered a robot.

#you can even break the capatch
https://medium.com/@ageitgey/how-to-break-a-captcha-system-in-15-minutes-with-machine-learning-dbebb035a710

#relevant xkcd
https://duckduckgo.com/?q=xkcd+1897&ia=comics

Answer 2

Captcha is distorted words, only the neurons of our human brain able to process the information.

Current common programs are yet to reach this recognition level.

Answer 3

how?
we are not robots

Answer 4

we'll see...

Answer 5

it was a joke refering to the dystopian future we are heading to

Answer 6

joke?