Where has common sense already failed?
I already have trust filtering, just by following specific journalists whose reporting I trust. They do the work of verifying photographs, because it's part of their area of professional expertise, and I appreciate it.
The intent of all trust systems is to make it more difficult (technically, financially) to falsify information. It’s a statistics game — the harder it is to break a trust system, the fewer people will do it. This is true for everything from house keys to PKI to currency to ID cards.
The general population doesn't care about whether an image was cryptographically signed. It's going to have zero effect.
People who don't care about the truth are going to continue to pass around edited images, while those who do get their news from trusted journalists and aren't paying attention to random images on social networks.
"Cryptographic trust" is never going to prove anything. Even if a camera can encrypt a photograph to try to prove a particular photograph was taken at a particular place and time, nothing is preventing someone from spoofing a GPS signal and snapping a photo of a doctored photograph with the camera.
Adulterated content has been around for basically as long as the printing press.