1. A computerized method for determining similarities between a first image and a second image using an image processing device, the method comprising: converting the first image into a first grayscale image and the second image into a second grayscale image, wherein the first image and the second image is prestored in a storage system of the image processing device, and a number of pixels of the second image is not less than the number of pixels of the first image; matching each pixel of the first grayscale image with a corresponding pixel of the second grayscale image to create a pixel pair sequence S={(Pi, P′j), 1≦i≦n, 1≦j≦m, n≦m,}, wherein the created pixel pair sequence S satisfies the conditions of: {(Pi, P′j)|ΣDij→min, 1≦i≦n, 1≦j≦m}, and Dij=|Vi−V′j|, Pi represents the pixel of the first grayscale image, P′j represents the pixel of the second grayscale image that is matched with the pixel Pi, n represents the number of the pixels of the first grayscale image, m represents the number of the pixels of the second grayscale image, Vi represents a grayscale value of the pixel Pi, and V′j represents a grayscale value of the pixel P′j; and calculating a similarity value indicating similarities between the first image and the second image according to the grayscale value of each pixel in the pixel pair sequence S.