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: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=None)

   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`:

Value Image format
'rgb' SGI ImgLib Files
'gif' GIF 87a and 89a Files
'pbm' Portable Bitmap Files
'pgm' Portable Graymap Files
'ppm' Portable Pixmap Files
'tiff' TIFF Files
'rast' Sun Raster Files
'xbm' X Bitmap Files
'jpeg' JPEG data in JFIF or Exif formats
'bmp' BMP files
'png' Portable Network Graphics
'webp' WebP files
'exr' OpenEXR Files 
.. versionadded:: 3.5
   The *exr* and *webp* formats were added.

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'