> In most scenarios Bob would be “trustworthy news source” who cares about their reputability. The important piece here is that if someone shares something on e.g. twitter and says Bob produced it, that claim can be verified.

We don't need some new system for that. You go to the website of your preferred news source and the connection is secured with TLS which certifies that the server is the one for the domain your browser shows you're visiting.

> Think about what happens today when a private key is leaked - that key is no longer trusted. Will it be such a large scale problem such that the day any camera is released the keys are leaked?

It's not that some camera's keys will be leaked and then you'll know not to trust them. It's that someone publishes how to extract the keys from some camera and then everything signed with any of those keys is called into question. Or figures out how to extract the keys from some camera or swipe them from one of the bureaucracies that generate them and doesn't tell anyone, they just use them to forge signatures.

And then because that is not only possible but likely to happen in practice, and you have no way to know when it has, you can't actually trust the signatures for anything.