We propose a real time tracking algorithm for a counting person application. Our algorithm needs any a priori knowledge neither on the model of person, nor on their size or their number, which can evolve with time. It manages several problems such as occlusion and under or over-segmentations especially thanks to a shape model obtained with a homography. The first step consisting in motion detection, leads to regions that have to be assigned to trajectories. This tracking step is achieved using a new concept: elementary tracks. They allow on the one hand to manage the tracking and on the other hand, to detect the output of occlusion by introducing coherent sets of regions. Those sets enable to define temporal kinematical, shape and colour models. Significant results will be presented on several sequences with ground truth.