Well if your guess is correct in 1 round, you 9x your input…

chryptof ·

Well if your guess is correct in 1 round, you 9x your input.
If your guess is correct in 2 rounds, you 4x your input.
Still with 4 rounds, you 1.5x your input.

I am sure there are at least 7+ images that you can guess in 1 round. So, your cost is 700 SAT, your gain is 6300 SATS.
I think it is a nice ROI %.