A system for automatic 2D/3D display mode selection is presented. Most 3D displays require special glasses to create an illusion of observing a 3D scene. The proposed system is using a camera to automatically detect if there are users in front of the display wearing the special 3D viewing glasses. An efficient algorithm is described to detect faces wearing the glasses in the camera images. Based on the detection, the display automatically switches between the 2D and 3D viewing modes.