The key difference is that digital signatures allow revocation-of-trust to be an effortless, automatic and delegatable process. As opposed to the current process that involves individual (and intrinsically limited) knowledge of who can be trusted. Frequently one doesn't even have provenance information for a media item, which is a prerequisite for making a trustworthiness judgment call.
The "hocus pocus" is literally the point that distinguishes this scheme from the plainly non-working system that we have today.
Just because something is different from something that doesn't work doesn't mean the different thing will work: most things don't work.
I'm not seeing anything in your description that couldn't also be said about using PKI to allow people to sign stuff they published. (And better: it's not broken by non-deceptive edits, like cropping or brightness adjustments)-- except that PKI already exists so we can't imagine that it would magically solve these problems. :) (and there is a long long history of people thinking varrious PKI ideas will magically solve varrious problems and then failing to solve them at all)
