A licence similar to a driving license seems like the way to go. It seems perfectly reasonable to require some training before being allowed a drone (for safety reasons). Each drone should have the electronic equivalent of a license plate for identification and if an owner is found to be using their drone in an illegal manner (laws to be determined...) then their license should be revoked.

There are incredible opportunities for doing cool things with drones, but a framework for managing their use seems perfectly reasonable to me.