In today's political climate, even with incontrovertible evidence, all you need to do is shout out at the top of your lungs: "FAKE NEWS", and it doesn't matter any more.
As national political news to a cynical, disinterested audience, fine.
But that's thinking too small: what happens when every recording of corporate misdeeds, every photo of a cheating spouse, even a child's baby pictures, lose their solidity as evidence? What happens to anonymous online conversations when "pics or it didn't happen" becomes "it didn't happen"?
We, as technologists, should come up with solutions that allow such shouts to become meaningless.