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：与输入数据建立人工智能系统有关的验证码请求不一定知道所有的正确答案。你可以给它提供不正确的答案，虽然你会失败几次，但它最终会让你通过，因为它不知道所有的图像是山/自行车/汽车等。