Can the photon be both massive and massless?

Theoretically, the photon is generally considered to be massless. On the other hand, experimentally many studies show that the photon can have a nonzero mass. Can the photon be both massive and massless? We have, following a semiclassical approach, shown that the photon can be both massive and massless. In contrast to previous studies of massive photon, the present approach is gauge invariant. The properties of both massless and massive photons are described by a set of field equations derived from a newly formed Lagrangian density. It shows that the value of photon mass is dependent on the photon's energy and the nature of the medium in which the photon travels. Numerical values of photon mass calculated from the present approach are essentially consistent with the experimental results obtained by previous investigators.