YSK: Captcha requests linked to feeding data to build AI systems do not necessarily know all the correct answers. You can feed it incorrect answers and, while you will fail a few times, it will eventually let you through because it does not know all of the images which are mountains/bikes/cars/etc.
from /r/YouShouldKnow
YSK：與輸入數據建立人工智能系統有關的驗證碼請求不一定知道所有的正確答案。你可以給它提供不正確的答案，雖然你會失敗幾次，但它最終會讓你通過，因爲它不知道所有的圖像是山/自行車/汽車等。