On a site note here, they don't need to be perfect. Well, sure, quality wise they have to be if they are to be hosted here as custom covers.
But design-wise or lets say aesthetically they don't have to be. I don't think that anyone else but me will use these custom covers. Whoever has the games would probably like a cover true to the original cover or in a different Super Famicom template. So if you have to tweak and tinker with the image to make it work in the US template that's fine. For everyone else the raws are still there, readily available to work with.