An interactive graphics system includes a touch-sensitive controller having a number of semi-transparent light-diffusing panels imaged by a rear mounted imaging device such as a video camera. The imaging device is arranged to detect the shadows of objects, such as fingers, touching any of the panels. The camera can simultaneously to detect multiple touch points on the panels resulting from the touch of multiple fingers, which facilitates the detection of input gestures. The panel and the position on the panel touched can be determined by the position of the shadow on the video image. As the imaging device is only required to detect the existence of shadows on the panels, only a two-dimensional image must be processed. However, since the imaging device can image multiple panels simultaneously, a multi-dimensional input signal can be provided. Further, as this image is of high contrast, only light/dark areas must be differentiated for greatly simplified image processing.