Make the scene more complicated and crowded. Increase the number of objects, details, or overlapping elements that might divert the player. They will need to focus more intently and carefully distinguish between important objects and background noise as a result of the increased complexity..
This game requires us to maximize our eyes. Sometimes, it is really hard for us to find which things that make two pictures different. The game is produced to trap us by giving a subtle and vague difference with the pictures.