1. An image-based coordinate input apparatus for detecting positions of N objects on a coordinate input region at a detecting interval, N equaling to 1 or 2, said image-based coordinate input apparatus comprising: a first image capturing device, disposed at a first location on the perimeter of the coordinate input region, for starting at the start of the detecting interval to capture successive first images relative to the N objects and a background of the perimeter of the coordinate input region; a second image capturing device, disposed at a second location on the perimeter of the coordinate input region, for starting at the start of the detecting interval to capture successive second images relative to the N objects and the background of the perimeter of the coordinate input region; a buffer, electrically connected to the first image capturing device and the second image capturing device respectively, for buffering the successive first images and the successive second images; and a processing unit, electrically connected to the buffer, for accessing the successive first images and the successive second images, judging a variation in accordance with the successive first images and the successive second images, and calculating the positions of said N objects on the coordinate input region at the detecting interval in accordance with the variation, the first images and the second images.