Nikon used to provide "Image Authentication Software" which would authenticate images and show if they had been altered since taken by the camera. This was useful not only in news but also court cases.

This, obviously, could not be used on tweaked published images but would work if you had access to the original frame. Most photojournalists work to a code whereby they don't amend the images at all, even tidying up, but that's only viable if they and their editors are trustworthy.

The Nikon process was cracked a few years ago. This allowed edited images to pass the validation.