Modern Python Standard Library Cookbook

How to do it...

The imghdr module can help us understand what kind of image file we are facing:

import imghdr


def detect_image_format(filename):
    return imghdr.what(filename)

This allows us to detect the format of any image on disk or of a stream of bytes provided:

>>> print(detect_image_format('~/Pictures/avatar.jpg'))
'jpeg'
>>> with open('~/Pictures/avatar.png', 'rb') as f:
...     print(detect_image_format(f))
'png'