Which pieces of C2PA are relevant to which kinds of users?

[lrosenthol]

From #12

Which pieces of C2PA are relevant to which kinds of users? E.g. maybe signatures by the camera and along the chain of provenance are more useful to content producers, while creator assertions are more useful to the average end-user. If we develop an ecosystem where fact-checkers can rate creators for accuracy, maybe those fact-checkers want to see a creator's justifications for endorsing a piece of content, so if a creator is tricked into signing something, the fact-checker can demote the people who tricked them instead of just the final creator.