Unless they check to see if the image is moving, which in the basic case would be easy to do. Of course, that can be defeated by substituting the still image with a short loop (presumably edited to eliminate any discontinuities), but that just escalates the arms race. Eventually, using an ad-funded website would involve volunteering one of your GPU cores to run a machine-learning model for authenticating camera video, and that’s just the price, along with accepting tracking cookies and disabling ad blockers.