I've heard this a lot in the context of news, but I don't know if I believe it.

You could say the same thing about words. Anybody can say anything online, but that doesn't mean you necessarily believe them. You cross-check their words with trusted sources and weigh what they say against what you believe to be rational and reasonable. I think people will just learn to do the same thing with photos and videos.

Plus there will likely be enough law suits around this to establish some kind of norm.