Functional? perhaps, but I would say that if one peer into history, what one finds is suspects convicted on evidence that would seem flimsy by today's standard, and so will the future look at us.

I would think that the number of false positive convictions declines with the advancement of new technology, and that this is perhaps a temporary setback.

There was a time before fingerprints and d.n.a. evidence as well, both of which have been very helpful not only in convicting the guilty, but in exonerating the innocent, and if ever come the time that it be feasible and affordable for a layman to plant fake d.n.a. evidence and fingerprints, that would be quite a setback for criminal forensics.

I think it's even simpler -- liars attracting any degree of press attention won't be able to get away with it.

"That picture was Photoshopped" doesn't work as a defense because it's not too difficult for experts to tell a Photoshop from a genuine image, nor to interview someone at the scene of an alleged event and learn the truth.

The same will be true with deepfakes, only much more so, because there are so many more ways to give away that it's a deepfake. Video adds new dimensions of scrutiny like how well the fake face tracks the head, matches lighting and expression, etc. Deepfake detection is in its infancy but you can bet it'll be even more accurate than Photoshop detection.