OAP,
I understand your concerns about witness statements, especially from traumatic events. Video is a very useful medium in cases like these, but my point is that, in many cases, you really need to understand where the camera was and the relative position of objects you're using as a reference.
In the example here of the speaker on a pole, a speaker mounted on a ten foot pole, ten feet from a six foot cameraman would appear to line up with an object at over 100 feet 100 yards away, roughly. Numbers done in my head using old money. As you don't know the height of the camera, the height of the speaker or the horizontal distance between any of the three objects, you can't do any sums to calculate the height of the aircraft. Get it?