In short, the game is poorly executed. You can't just expect average players to get the code by giving a hardly pixelated picture with no precision whatsoever. That's alienating them from trying the game and matter of fact, I do think your game has low download count just because of that same reason. You should rather focus of gameplay than the difficulty of a puzzle. That's my advice to you, either take it to the bank or disregard it, your choice.
Best of luck with the future games.