1. An interactive input system comprising: imaging devices with different viewpoints and having at least partially overlapping fields of view of a touch surface, at least one of the imaging devices comprising first and second adjacent image sensors with different focal lengths, the first image sensor having a field of view encompassing generally the entirety of the touch surface and the second image sensor having a field of view encompassing only a portion of the touch surface; and processing structure configured to process image data acquired by the imaging devices to determine if a pointer image exists in the image data with a desired level of confidence and generate pointer data, wherein for each of said at least one imaging devices having said first and second adjacent image sensors with different focal lengths, said processing structure configured to generate the pointer data using image data acquired by only one of said first and second adjacent image sensors and to determine the location of a pointer on the touch surface based on the pointer data, wherein for each pointer contact with said touch surface at a location that is proximate the at least one imaging device, the pointer image is determined to exist in the image data with the desired level of confidence in only image data acquired by the first image sensor, and wherein for each pointer contact with said touch surface that is distant from the at least one imaging device, the pointer image is determined to exist in the image data with the desired level of confidence in only image data acquired by the second image sensor.