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

================================================

.. module:: imghdr

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

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`:

+------------+-----------------------------------+

| 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         |

+------------+-----------------------------------+

.. 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('/tmp/bass.gif')

   'gif'