Yes and no. Yes, E=mc^2 does still apply, but this refers only to a particles rest energy. So in the rest frame of a photon, the photon has no energy, and thus

Yes and no. Yes, E=mc^2 does still apply, but this refers only to a particles rest energy. So in the rest frame of a photon, the photon has no energy, and thus has no mass (or at least that's the theory, in principle more difficult to test and for all intents and purposes it is very nearly zero and most probably is exactly zero). In our rest frame, the photon moves at the speed of light, so... E = mc^2 + kintetic energy + potential energy -> which basically reduces to E = hf (plank's constant * frequency of the light).