>>527989894
Found what I was looking for with the first resource. What I meant by backgrounds was the image that displays when you launch the game. Picrel is an example of one. It's a PS2 game bundled in with an emulator, so without specifying a background, it's just display the PS2 background before starting the game.

I looked further into it, and I guess I was mistake; I don't need a cover nor background, it apparently auto-populates--at least according to pkgviewer. It doesn't have the exact cover, but it does already have one. I guess it's just necessary to do so with PS2 games converted to fpkgs. There's probably some way to choose my own cover art.