Actually i never help google to work for free.
Answer X-1 fields correctly and one totally not. Gotta do it twice at least, but be consistent.
For one captcha they know the answer, for one they don't. You're working by helping them identifying objects in that one. Don't đ
Dunno. But why else should they offer such thing "for free"? What else gainful there is in millions of people identifying millions of images? If it's not for training AIs, i would have no better idea :)
The first one I ever saw was put animals in the direction of an arrow. It wasnt always clear if they are supposed to be in that direction now and when you took too much time you had to do it again