The paper proposes a simple, economical and efficient real-time, visual hand gesture recognition system for human-computer interaction. The system is designed to work in critical lighting conditions, for example when an image is projected onto a wall (conferences, offices, etc). Given the low level of computational complexity, the system can be used instead of a mouse. The extreme naturalness of the interaction makes previous training unnecessary and the robustness of the algorithms used guarantees a high level of reliability. The architecture of the system is described, and experimental results obtained in a large number of tests with different, untrained users are presented and commented.