I'm thinking about purchasing Forza 4 for Xbox. I know I can "customize" my car's paint job in the game, but is it possible to upload my own images/decals to the game to put onto my car? Say, something like a company logo or a picture of my dog?
Officially, there's no way about to do it.
You can't. All images you see are carefully constructed using various shapes and tools within the game.