true-name.py

#!/usr/bin/env python3
import imghdr
import glob
from sys import argv
from pathlib import Path

pattern = '/Users/uonr/Pictures/*';
print(pattern)

for filepath in [Path(p) for p in glob.glob(pattern)]:
    if filepath.is_dir():
        continue
    with open(filepath, 'rb') as f:
        what = imghdr.what(f)
    if not what:
        continue
    rename = filepath.with_suffix('.' + what)
    if rename == filepath:
        continue
    print(f'rename {filepath} -> {rename}')
    filepath.rename(rename)