1. A method for detecting objects crossing a virtual boundary line comprising: defining a virtual boundary line in a region of interest; establishing a set of ground patch regions surrounding the virtual boundary line; extracting a set of attributes from each of the set of ground patch regions; updating a ground patch history model with the set of attributes from each of the set of ground patch regions; and analyzing the ground patch history model to detect whether an object captured in at least one of the set of ground patch regions is crossing the virtual boundary line in the video region of interest.