1. A computer-implemented method for processing an image file using a computing device, the method comprising: (a) reading an image file from a storage system of the computing device; (b) determining whether an image in the image file is slanted, the image in the image file comprising one or more characters; (c) calculating an incision coordinates of the image according to initial incision coordinates and initial increment coordinates in a predetermined configuration file stored in the storage system and a preset formula, if the image is determined to be slanted, or executing step (e) if the image is determined to be not slanted; (d) incising the image using the calculated incision coordinates and storing the incised image in a new image file, and returning to step (b) to determine whether the incised image in the new image file is slanted; (e) determining whether the image has been incised; (f) recording the calculated incision coordinates that make the image not be slanted as optimal incision coordinates and storing the optimal incision coordinates into the storage system, if the image has been incised.