This creates and interesting question.
What, then, can we accept as proof?
Unfortunately, in terms of any sort of third-party source, as in videotape, photographs, and audio, nothing can be accepted anymore. I'm afraid the acceptability of photo and video evidence in court cases is not long for this world either. Artifacts don't mean anything, not when you have hobbyists who make so-called artifacts for a living.
Technology and the ability to make cool home movies is a double-edged sword. Today anyone with a Mac or PC and a piece of software can create footage that is so genuine-looking that were it shown even a decade ago it would have been physically impossible to debunk on its own merits. And that's homemade stuff. Add a budget to it and it's even more real - people still think the Sci-Fi channel's "UFO over the World Trade Center" commercial (from a year or 2 before 9/11) is genuine and I've seen people abjectly refuse to believe otherwise. Even though you'd think a UFO buzzing downtown NYC would have been seen and captured on other cameras if it were real.
The Death Star in San Francisco footage is amazing, and it's ancient in the context of technology. It also shows how footage of other events - in this case a protest rally - can be manipulated quite easily to refer to something else:
http://www.youtube.com/watch?v=AfqDVP_0O0c
It is a shame because it's going to hurt people who might legitimately catch something of interest. And yes I know you can run tests to prove whether certain footage is real, even with digital enhancements. But as far as "proving UFOs exist," the public will never be able to buy it unless a massively public event - such as that depicted in V and Independence Day - were to occur.
PS. I know the thread-starter asked for faked footage to not be posted, but in the context of answer the "what can be used as proof" question, I feel an example needs to be given.
Alex