1. A method for determining if an input image is a foggy image, comprising: determining an average luminance gray level of the input image; performing Sobel image processing on the input image to generate a Sobel image of the input image when the average luminance gray level of the input image is between a first image average luminance and a second image average luminance; determining a first normalization value and a second normalization value of the input image; determining a mean value and a standard deviation of the Sobel image when the first normalization value and the second normalization value are less than a first threshold value; and determining the input image as a foggy image when a sum of the mean value and the standard deviation is less than a second threshold value.