Plastic surgery was used to smooth out the minor differences. They failed to fix a scar on Campbell's upper lip - this is how you can tell authentic McCartney photos from the Campbell ones. Most of the clues are very ambiguous. The certainly do not offer concrete evidence as to whether or not they were planted or simply coincidental. Most of the clues can be refuted wither way.
Nobody knows for sure.
I am certain that each Beatle has publicly denied having anything to do with the hoax. I am also certain that Paul is NOT dead - I saw him in person a few years ago.