Imagine you open Twitter and see a video of someone committing a crime. That could very well be a real photo of a real event. But the event might not have been a crime. Or it may not have been real at all. Or the footage might be from something else entirely. Remember that time few years ago around an air crash investigation when people believed they've seen footage from the plane breaking up, only it turned out someone just posted a scene from LOST? Or recall these one or two heart-breaking pictures of people suffering that surface on Facebook every time there's some fighting going on, always labeled "evil side $X did this in city $C"? Those are always the same pictures of some one event that happened long time ago, but people read them as "evidence" of new atrocities.
Now obviously courts don't view social media posts in a binary way. Enough investigators and expert witnesses can work on a social media post until it has the colour of evidence.
 - https://ansuz.sooke.bc.ca/entry/23