A handwriting system includes a light source module, an image sensing apparatus and a processing circuit. The light source module is configured to provide a light source to illuminate an object on a plane. The image sensing apparatus is disposed on the plane and configured to capture an image of the object reflecting light emitted by the light source. The processing circuit is electrically connected to the image sensing apparatus and configured to receive the image captured by the image sensing apparatus, analyze the shape of each of light spot(s) in the captured image and screen out the light spot(s) not conforming to the shape of the object. Another handwriting system and two handwriting system operation methods are also provided.