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 :>