Provenance and chain of custody is everything. It's always been important, but now its critical. Any audio or video without a solid chain of custody is now suspect. Anonymous leaks are worthless as anything can be faked by almost anyone with a PC.
Old and busted: "pic or it didn't happen."
New hotness: "in person witness or it didn't happen."
Cue 10 ICOs for AuthenticityCoin type things, most of which just exit scam and the rest of which don't actually work.
The real security hole for forgery is at the point of injection. Tracking a forgery along with a block chain doesn't prove it's not a forgery.
One thought is a camera sensor that cryptographically signs (watermarks) photos or video frames on the sensor before they are touched by anything else. It's not perfect since a highly sophisticated adversary could get the secret key out of the chip, but it could definitely make it quite a bit harder to fake photos. Nothing is ever perfectly secure. All security amounts to increasing the work function for violating a control to some decent margin above the payoff you get from breaking the control.
I could see certified watermarking camera sensors being used by journalists, politicians, governments, police, etc.
This is a start. It can even be done steganographically, embedded in the picture in a non-visual way, which is robust against compression and "social media laundering" (term of art for uploading then downloading from social media).
The problem is people just don't care. See "cheap fakes" like slowing down a video of Pelosi and claiming she's drunk. People actually believe that garbage. No amount of fancy math can fix that.
Old and busted: "pic or it didn't happen."
New hotness: "in person witness or it didn't happen."