What does "Potato Cat" mean when you point this to a person?

Solution 1:

This phrase is due to the popularity of a card game designed by the online cartoonist known as "The Oatmeal - the game is called "Exploding Kittens" and is now commonly played in households with children from just pre-teen through teen ages - some young adults have also adopted this game.

Potato Cat is a specific category of card in this game, which is intrinsically useless on its own, having no specific ability or action assigned to it; however, when assembled with other Potato Cat cards, can be used to demand a card from another player's hand. I'd guess half the reason this is used in the context of photos is visual...