In the case of the Anasazi Drawing, which is the one I'm most familar with, the claim is not that the drawing is fraudulent but that the authors of the articles are frauds or at least wilfully deceiving themselves.
The drawing appears to be a very common motif that I personally have seen many times while wandering around the Southwest. Time, ligting, weathering and frankly, the guy that touched up the photo turned a comon serpent glyph into a mockery of a dinosaur.
I don't doubt that the glyph exists and that it's probably from the Anasazi. It's the total dishonesty or gulibility of those trying to make it into a dinsosaur that is questioned.
Aslan is not a Tame Lion