I don't imagine that there can be any way to automatically determine a proper cover. Basically the check would come down to something like "Is page 1 an image? If Yes, assume it's the cover image, rename accordingly." The problem is that it might instead be advertising, a map, a legitimate cover - that has become corrupted, a foreign language cover, etc.
The really odd thing about your request is that a few years ago we were all asking Kovid & Co to allow the user more choice in covers/cover generation. Now we've got it and we're swinging back to automation.
