I was taken in by the fake Kerry/Fonda photo when it first appeared, but only for a short while. Seemed to me at the time that the existence of the fake actually boosted the attention given to the real photo that I saw shortly afterward.
Let me give you a tip that may be comforting: Lies certainly propagate faster than truth, but they all have something that the truth does not have: a short expiration date. Truth does not expire.