This paper presents a vision-based interface system, VISUAL PANEL, which employs an arbitrary quadrangle-shaped panel (e.g., an ordinary piece of paper) and a tip pointer (e.g., fingertip) as an intuitive, wireless and mobile input device. The system can accurately and reliably track the panel and the tip pointer. The panel tracking continuously determines the projective mapping between the panel at the current position and the display, which in turn maps the tip position to the corresponding position on the display. By detecting the clicking and dragging actions, the system can fulfill many tasks such as controlling a remote large display, and simulating a physical keyboard. Users can naturally use their fingers or other tip pointers to issue commands and type texts. Furthermore, by tracking the 3D position and orientation of the visual panel, the system can also provide 3D information, serving as a virtual joystick, to control 3D virtual objects.