1. An image processing method, comprising: receiving a video stream, wherein the video stream comprises an image that includes a plurality of regions each comprising a plurality of pixels, wherein each pixel has an associated gray-scale value; determining, for each of the plurality of regions, a maximum gray-scale difference representing a difference between a maximum gray-scale value of the region and a minimum gray-scale value of the region; determining, for each of the plurality of regions, a gray-scale variation level based on the corresponding maximum gray-scale difference; wherein determining, for each of the plurality of regions, a gray-scale variation level is further based on an absolute gray-scale difference representing a difference between a selected gray-scale value of the region and a median gray-scale value of the region; determining whether the video stream comprises a converted image converted from a low-resolution image to a high-resolution image based on the gray scale variation levels for the plurality of regions; and performing image quality enhancement on the video stream when the video stream comprises the converted image converted from the low-resolution image to the high-resolution image.