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) when the image is determined to be slanted, calculating an incision coordinates of the image according to initial incision coordinate and initial increment coordinates in a predetermined configuration file stored in the storage system and a preset formula, ending the method when 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 determining whether the incised image in the new image file is slanted; (e) when the incised image is determined to be slanted, calculating an incision coordinates of the incised image and returning to (d), and when the incised image is determined to be not slanted, recording the calculated incision coordinates corresponding to the incised image as optimal incision coordinates and storing the optimal incision coordinates into the storage system; (f) when a number of the optimal incision coordinates in the storage system exceeds a preset number, updating the predetermined configuration file by extracting first optimal incision coordinates having the highest frequencies in the storage system to replace the original incision coordinates in the predetermined configuration file, and calculating difference coordinates between the first optimal incision coordinates and second optimal incision coordinates having the second highest frequencies in the storage system, and replacing the initial increment coordinates by a half of the difference coordinates.