I demo with different parameter here:
detector.MergeThreshold = 5;
detector.ScaleFactor = 1.1;
detector.MinSize = [50 50];
-> It is not quite good yeah :<
detector.MergeThreshold = 5;
detector.ScaleFactor = 1.01;
detector.MinSize = [20 20];
-> It is sometimes can detect some ghosts, even in the morning :>