Beginning moving objects: When an object initially in the background moves, both it and the newly revealed parts of the background called "ghost" are detected.
Sleeping foreground objects: Foreground object that becomes motionless cannot be distinguished from a background object and then it will be incorporated in the background. How to manage this situation depends on the context. Indeed, in some applications, motionless foreground objects must be incorporated and in others it is not the case.
Slow movinf foreground objects
Small foreground objects