I assure you that photo authenticity is not an emerging field.
Using cryptographically signed photos is not even new, most of the major camera manufacturers are offering it, or are working on offering it at this point. The reality is that even with things like sensor depth data proving that a scene is in 3 dimensions, you are still able to manipulate the actors in a scene, still able to selectively include or exclude elements, still able to pick the image that seems to show something that it doesn't, still able to editorialize in a text description of a scene etc.
The time-proven solution for this is to rely on institutional reputation. While every news source has had lapses, I am far more likely to trust the reality and neutrality of, say, the AP over Fox News regardless of the presence of a signature.
Disclosure: I used to freelance for the AP as a photojournalist.
It's an emerging field, and attack vectors like that are hurdles to be solved. You can make faking more difficuly, for example, with a depth sensor.