uniqueMD5

import hashlib
import os
file_names = os.listdir("Captcha/")
key = {}
file = open("result.txt","w")
for i in xrange(0,len(file_names)):
    key[hashlib.md5(open("Captcha/"+file_names[i],"rb").read()).hexdigest()] = file_names[i]
json.dump(key,file)