Greetings from the Australian National University "Information & Human Centred Computing" where Dr Sabrina Caldwell is talking on "Digital Image Credibility".
To provide credible photographs Dr Caldwell suggests camera could record biometric information about the photographer, characteristics of the image sensor of the camera (to identify the camera), the processing of the image in the camera, and later. The image could be watermarked or have a digital signature to prevent tampering.
One technique which occurs to me is that the characteristics of the lens used could also be used to identify the camera used (this would work on old analogue cameras as well as digital ones).
What was not clear to me is why it would be considered to be worth preserving the false impression the public has that digital photos can be relied on. It would seem to me to be better to educate the public that digital photos are easily manipulated and should not be relied on for more than entertainment. It would be useful to have ways to authenticate photographs used for legal and scientific evidence.
Dr Caldwell suggests wrapping extra metadata up with an image, to show how it was constructed. This could be very useful.
There may be alternative ways to verify how "real" an image is. For example truth could be crowd-sourced: rather than depend on one photo, a large number of photos claiming to be of the same thing could be compared.