The appropriate generalisation of the classical image force to quantum mechanics is discussed. Photon assisted tunnelling and internal photoemission are discussed in the light of this generalisation. Essentially, the qualitative result is that the quantum mechanical image force potential is reduced from the classical result by the transmission probability of the interface. As a consequence, no image force is expected in photon assisted tunnelling, whereas essentially the classical result is expected in internal photoemission. This result is in qualitative agreement with experiment.