I wondered before why with all these pictures of Harry's parents and Dumbledore that none of them talked. Now I understand that photos don't talk and those in them don't move between like they do in paintings. In Chapter Fifteen Phineas Nigellus explains that portraits within Hogwarts may move between other portraits, but can't go beyond Hogwarts, except to visit a painting of themselves that is somewhere else.

It might have been explained before, but this time it finally sunk in Helpful tid-bit.