I remember when snapchat were touting "send picture that delete within timeframes set by you!" and all that would happen is you'd turn to your friend and have them take a picture of your phone.
In the above case, the outcome was messy. But with some effort, people could make reasonable quality "certified" pictures of damn near anything by taking a picture of a picture. Then there is the more technical approach of cracking a system physically in your hands so you can sign whatever you want anyway...
I think the aim should be less on the camera hardware attestation and more on the user. "It is signed with their key! They take responsibility for it!"
But then we need:
1. fully active and scaled public/private key encryption for all users for whatever they want to do
2. a world where people are held responsible for their actions...
I'm not sure which is more unrealistic.