1. A computer-implemented image classification method executed by a computer, comprising: obtaining an image using the computer; processing the image, using the computer, by at least one of calculating an average color difference between at least one average channel value of pixels in at least one boundary region of the image and a predefined standard value, calculating a gradient variation magnitude difference between at least two regions of the image, and calculating a percentage of the edges of the image to the image; and classifying the image, using the computer, according to at least one of the average color difference, the gradient variation magnitude difference, and the percentage of the edges of the image to the image.