A touch system includes a touch surface on which an image is, displayed and at least one camera acquiring images of the touch surface. A pointer contact data generator generates pointer position data in response to pointer contact with the touch surface. The pointer position data represents the location of the pointer on the touch surface where pointer contact is made. A processor communicates with the at least one camera and the pointer contact data generator. The processor uses known points in the displayed images to calibrate automatically co-ordinate systems of the touch system, and uses calibrated pointer position data to update image data that is used to present the displayed image on the touch surface. In one embodiment, the touch system includes an active touch sensitive screen that comprises both the touch surface and the pointer contact data generator. In another embodiment, image data generated by a pair of cameras having overlapping fields of view is used by the pointer contact data generator to generate the pointer position data when a pointer is acquired in images captured by the pair of cameras.