'Spot the ball' was a staple of local newspaper competitions - an action shot of a game with the ball removed by presumably pre-digital photographic trickery. Entrants were invited to mark a cross where they thought the ball might have been, and the closest to the original centre co-ordinates won a prize.
So yeah, surprisingly tricky, but you could set up a big training set along similar lines.
I've seen that online with big costs for guesses and prizes. Many years ago but I'm sure it is still around. I thought about how to computationally determine the ball position until I read that the ball position was decided by an impartial referee's opinion.
So yeah, surprisingly tricky, but you could set up a big training set along similar lines.