fluffyvoidwarrior,
I had contemplated writing software once to analyze security footage to determine if there was anything worth a human looking at. The idea was that a stationary camera recording a room with no activity should really just be a series of nearly identical still images. If any image looked different enough from the others it meant something came into view of the camera.

I don't know if a similar technique would work here without seeing samples both of the "ok" and the "foreign" shots.