A system recognizes user-object gesture interactions with the surface of a monitor display, with hover space defined spaced-apart from the display surface, or in virtual scroll regions defined on the periphery of the monitor display. The system recognizes user-object interactions, e.g., gestures, and can affect what is displayed commensurately. The system includes at least a first time-of-flight (TOF) system and at least one of a second TOF, a two-dimensional camera, and a mirror, each TOF system processing at least one of z-depth data and A-brightness data. User-object interactions, e.g., touching(s) of the display surface, location(s) in a hover region, or location(s) in a virtual scroll region, are recognized passively in that the user-object need not have capacitance, resistance, exert force, or deform during gesture interaction. The system may be attached retroactively to the monitor, which may be a large (>22 cm) monitor, or a small cell phone sized monitor.