[6mian]

In visible range, would. The technique shown in the video work not perfectly clear sky conditions? Clouds are not uniform layer that moves with exactly the same speed in each point.

Are there reliable ways to figure out which pixels on subtracted frames are cloud movement and which are the few ones that are an aircraft?

Correct me if I'm wrong, but adding extra cameras doesn't seem to solve this problem, each source reporting "almost everything moves" would make solving intersections and tracking them impossible, because each target candidate can be assigned to many changes pixels in consecutive frames. Unless some additional pattern detection is done, but again it's hard for very small objects.