import numpy as np

def mc(img1, img2, border_size):
    x1, y1 = img1.shape 
    x2, y2 = img2.shape 

    if (x1, y1) != (x2, y2):
        print "Images de tailles differentes !"

    ext1 = img1[border_size:x1-border_size, border_size:y1-border_size]
    ext2 = img2[border_size:x1-border_size, border_size:y1-border_size]
    r = np.mean((ext1 - ext2) ** 2)
    return r