With files being deleted by the DOJ and conspiracy theories and fake photos rising. Is their a way to prove authencity of existing but deleted files?

I mean I know that people will have back-ups on their devices etc. But with the current crazyness what stops Trump from calling everything a hoax and specific files "fake news"? Is there a way to properly verify the integrity of the downloaded files? Obviously this envolves major misstrust against the FBI/DOJ but I guess that's well earned by now.

I wish all the Americans the strength to stand up and fight against this crazyness. Its already horrible to whitness this from Germany/Europe but I can only imagine it's even worse for any American! Stand up for your rights and country and let them pay. Europe will follow your lead!