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At the end of each course, you have to pick one picture of each Pokémon that you will show to Oak. He judges them by 5 categories and gives you the score:

Special Pictures - Some pictures are special pictures that Oak gives a name to. Examples: "Surfing Pikachu", "Pikachu on a Stump", "Graveler's Group Dance", "Rare Pokémon Mew", etc.

Size - The bigger the Pokémon, the higher your score will be. But don't make it go out of the screen, that would reduce your score. 1000 is the best score you can get for size.

Action - Don't take a picture of a Pokémon doing nothing at all. Try to make it do something. Items work well. Never take a picture of a Pokémon from behind.

Position - Your score id doubled if the Pokémon is in the center of the frame.

Same Pokémon - If you get more than one of the same Pokémon in the picture, Oak gives you a small bonus depending on how big or how many extra Pokémon are present.