1. A grinding method to be implemented by a system that includes an image-capturing device, an image-processing device, a controlling device, and a grinding device, said grinding method comprising the steps of: A) placing a workpiece on a platform of the grinding device; B) enabling the controlling device to control grinding of the workpiece by the grinding device; C) enabling the image-capturing device to capture a set of consecutive images containing the workpiece being ground by the grinding device; D) through a motion detection algorithm, enabling the image-processing device to identify the workpiece from the images captured in step C); E) enabling the image-processing device to detect a top edge of the workpiece identified in step D) from a latest one of the images captured in step C); F) enabling the image-processing device to locate a set of image pixels, each of which lies on the top edge of the workpiece detected in step E); G) enabling the image-processing device to determine relative heights of the image pixels located in step F); and H) enabling the controlling device to control relative movement between the platform and a grinding unit of the grinding device with reference to the relative heights of the image pixels determined in step G).