At best, that that setup lets you prove that a certain pattern of light was present on the camera sensor at a certain time. It says nothing about the way the pattern was created, whether it was pointed at a real scene, or whether someone projected a faked movie into the camera.

By extension, any scheme to prove the truth of arbitrary measurements (audio, video, anything else) is vulnerable to manipulation of the measured value itself. The only way to be sure that something isn't fake is to experience it yourself (at least until virtual reality improves far enough to make even personal experience unreliable).