Asking this question I assume the example photons travel in vacuum. Once a source emits a photon they get separated by some space. Doesn't that space expand with the Hubble constant like the rest of the universe? If it does (even very slightly when the distance is small) can we assume that every photon travels with superluminal speed away from its source after any meaningful time has passed from emission?
As a secondary question: would the total relative speed of the photon be a simple addition of the speed of light and the product of the Hubble constant and the proper distance between the source and the photon?