1. A scanning device, comprising: a scanning platform for supporting an object, wherein a reference origin is defined on the scanning platform for positioning the object; and an optical chassis, located at a detection position, comprising: a carriage; an image sensor disposed in the carriage for capturing an image of the object and generating image data of the object; and a detector set, mounted on the carriage for detecting the presence of the object at the reference origin, wherein the detector set comprises: a first detecting unit extending along a first axis; and a second detecting unit extending along a second axis, wherein the second axis is substantially perpendicular to the first axis.