People generating fake photos will just use an AI that doesn't leave a watermark. We are quickly approaching the point at which AI-generated and real images just cannot be distinguished, and we're going to have to adapt to that.
There have been attempts to cryptographically sign images, which have largely been broken, but the principle is there: https://www.dpreview.com/opinion/9955873926/why-cryptographi...
If the plan is to have a few trusted manufacturers for CCTV and police cameras than that might work, but will do little to combat misinformation.
Eh, there are so many ways where a large photo can fail. I'm obsessed with AI Art, but I think there will be human(or AI) detectors that will be paid to determine validity.
I don't see how we can without great harm. The only adaptation that I can see is to stop trusting in anything at all, and we're already dangerously far down that road as it is.