As I understand it, it’s a digital signature scheme where the raw image is signed at the camera, and modifications in compliant software are signed as well. So it’s not so much “this picture is 100% real, no backsies”. Nor is it “We know all the things done to this picture”, as I doubt people who modify these photos want us to know what they are modifying.

So it’s more like “This picture has been modified, like all pictures are, but we can prove how many times it was touched, and who touched it”. They might even be able to prove when all that stuff happened.