In this paper, the Prewitt Algorithm is employed to detect the edge boundary of the given apple image, and then threshold segmentation is employed to segment it, finally, To determine whether the apple has scars by calculating regions, this method can remove the shadow of apple, its speed is very fast, The experiment results show that the method can locate the scar and stem areas of the apple images, operate easily and has well practicability. Testing of the method was performed with 100 samples, and the overall correct classification rate obtained was 99%. The method had two major advantages. It produces high performance, and it also eliminates the shadow of samples.