This is 'supposed' to find all images without extension in the current directory and put the appropriate extension on them.

imgnamer.py

#!/usr/bin/env python
import os, imghdr
dlist = os.listdir("."+os.sep)
for x in dlist:
    endr = imghdr.what(x)
    endr = str(endr)
    if endr == "None": continue
    elif x[(len(endr)*(-1)):] == endr: continue
    else: os.rename(x,x+"."+endr)