Comment by Metricon

There are a number of ways this might get solved, but I would speculate that it will generally be solved by adding image metadata that is signed by a certificate authority similar to the way SSL certificates are assigned to domains.

I think eventually all digital cameras and image scanners will securely hash and sign images just as forensic cameras do to certify that an image was "captured" instead of generated.

Of course this leaves a grey area for image editing applications such as Photoshop, so there may also need to be some other level of certificate base signing introduced there as well.