I was opening a couple of game boy games because I was after a case to use with a project. (I will make a post about that project later.) I noticed that I had a couple of pirate carts so I decided to photograph their pcb´s because they looked a bit different compared to the official game boy carts pcb´s. You can often recognize pirate game boy carts by the text at the top of the cart. Official carts should say "Nintendo GAME BOY ™". If it says something else than that its most likely a pirate cart. They sometimes only have the word "GAME" or "GAME BOY" at the top.
The grey one at the top here is the game "Mortal Kombat 4" which is probably one of the worst games ever made for game boy. The yellow one beneath the grey one is the game "The Mummy". I can´t recall ever playing it though but movie based games are hardly any good, but of course there is a few exceptions. It also came in a different shape of yellow compared to nintendos original yellow carts like Pokémon Yellow, Donkey Kong Land 2 etc...)