Interactive multimedia display has attracted great attention in recent years. However, most of the existing systems lack the user-aware capability, i.e. blind to the viewer's height and spatial location in a real-world 3D space, and often fail to provide a natural interaction. Therefore, in this work, we propose a probabilistic framework for detecting the viewer, (i.e. human heads) in depth images from a bird's eye view camera. In comparison to the state-of-the-art approaches, the experimental results demonstrated that the proposed framework can provide higher detection rate but also real-time execution. Even a large number of people are walking or standing together shoulder-by-shoulder, the proposed probabilistic head detection scheme is still able to give promising people detection capability.