But then what? So you have a camera signing its files and we pretend that extraction of the secret key is impossible (which it probably isn’t). You load the file into your editing program because usually, the source files are processed further. You create a derivative of the signed file and there’s no connection to the old signature anymore, so this would only make sense if you provide the original file for verification purposes, which most people won’t do.

I guess it’s better than nothing but it will require more infrastructure to turn it into something usable, or of this was only used in important situations where manual checking isn’t an issue, like a newspaper posting a picture but keeping the original to verify the authenticity.