What do you call the painted image done on a car? I think there's a specific terms used by people who do the paint job for custom cars, but I can't remember what it was.
You probably mean "decal" (from French décalcomania, from décalquer = tracing). These are not actually painted but transferred: An image is printed on special paper and it can be transferred from the paper to the body of the car with water. It allows for complex designs to be produced quickly without needing the same level of skill that direct painting requires.