After watching the scene several times, I fully believe it's a future incarnation who took the face of a past one. The Doctor finds Gallifrey (probably at the end of the next season) and eventually returns the painting to Earth, though we may well not see that.
Personally I'm thrilled Gallifrey is back from the abyss, well at least partially. Opens up a bunch more story possibilities.
I'd imagine even RTD eventually planned for Gallifrey to be restored.