Natural Human-Computer Interaction (NHCI) was hypothesized in the nineties as a solution to close the gap between computers and systems. It claims for interfaces that can be used in a natural and intuitive way through non intrusive and invisible input sensors, exploiting advances and results of pattern recognition, and image and speech understanding. This paper presents a multiuser natural interaction system that supports cooperative interaction in the manipulation and management of multimedia objects. The system uses a computer vision module to recognize and analyze hand gestures made by several users over a shared large display table.