:mod:`imghdr` --- Determine the type of an image

.. module:: imghdr
   :synopsis: Determine the type of image contained in a file or byte stream.

Source code: :source:`Lib/imghdr.py`

The :mod:`imghdr` module determines the type of image contained in a file or byte stream.

The :mod:`imghdr` module defines the following function:

.. function:: what(filename[, h])

   Tests the image data contained in the file named by *filename*, and returns a
   string describing the image type.  If optional *h* is provided, the *filename*
   is ignored and *h* is assumed to contain the byte stream to test.

The following image types are recognized, as listed below with the return value from :func:`what`:

.. versionadded:: 2.5
   Exif detection.

You can extend the list of file types :mod:`imghdr` can recognize by appending to this variable:

.. data:: tests

   A list of functions performing the individual tests.  Each function takes two
   arguments: the byte-stream and an open file-like object. When :func:`what` is
   called with a byte-stream, the file-like object will be ``None``.

   The test function should return a string describing the image type if the test
   succeeded, or ``None`` if it failed.

Example:

>>> import imghdr
>>> imghdr.what('bass.gif')
'gif'