Thats because reCAPTCHA originally started as free labor, or “mass collaboration project” to digitalize books where words are too illegible for computer. then google bought it for anti bot and bot training.
This is why V1 has 2 words, 1 word is control word (the system knows is true) and the other one being unknown. so when a person types the correct first word, it is assumed the second one is true, and it gives it point. and when enough people give the same second response to the 2nd words, the system “learns” that second word and puts it into control.
Since then, the purpose was moved from learning words to actually blocking bot activities AND learning user behavior. modern Captcha actually runs in the background and analyses your activity to distinguish it from human and bots.
Those picture puzzles? yeah purpose 1 is to block dumb bots, and purpose 2 is to train AI learning.
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