A user input method includes the following steps. A virtual keyboard layout and a control region are displayed. The virtual keyboard layout includes a plurality of key subgroups each mapped to a respective one of a plurality of regions of the control region. Locations of an object from at least one captured image are extracted to identify a location of a feature point of the object. A target region in which the feature point is located is determined. Keys mapped to the target region are determined. Movements of the object are translated as input data to the user interface system.