DEMO：

# -*- coding:utf-8 -*-
import os
import md5

def rename(path):
    os.chdir(path)
    for f in os.listdir(path):
        newname = getMD5(f)
        os.rename(f+"", newname+".jpg")
        print(newname+".jpg")

def getMD5(src):
    m1 = md5.new()   
    m1.update(src)   
    return m1.hexdigest() 

if __name__ == '__main__':
    path = 'D:\\wallpaper'
    rename(path)