In a method for scanning edges of an object using a computing device, the computing device is connected to an image measuring machine including an image capturing device. A start point, an end point, a scan direction, and a scan distance interval are set. Scan points on the edges of the object are determined. For each scan point, the computing device aims the image capturing device at the scan point, controls the image capturing device to capture images of the object at different depths, and records focal points. Definition values of the images are calculated and an image with a highest definition value is determined. A focal point corresponds to the image with the highest definition value and so coordinates of the scan point are determined. Scanned edges of the object are formed based on all the scan points.