1. A computer-implemented process for transforming a computer screen into a touch screen using a camera, comprising using a computer to perform the following process actions: inputting images of the computer screen; computing a projective mapping between the images and the screen which is capable of determining the screen coordinates of a point in the images; locating a tip of an indicator in said images, said indicator being superimposed on the screen in the image; and determining the position of the tip of the indicator on the screen from the images of the screen using said projective mapping.