1. An interactive input system comprising: an optical waveguide; a radiation source directing radiation into the optical waveguide, the radiation undergoing total internal reflection within the optical waveguide in response to at least one touch input on a touch surface of the optical waveguide; at least one imaging device positioned adjacent to the optical waveguide and having a field of view looking inside the optical waveguide and capturing image frames thereof; and processing structure for processing the image frames to determine a location of the at least one touch input based on a frequency of reflections of the radiation in the image frame.