
``imghdr`` --- Determine the type of an image
*********************************************

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

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

imghdr.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 ``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           |
+--------------+-------------------------------------+

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

imghdr.tests

   A list of functions performing the individual tests.  Each function
   takes two arguments: the byte-stream and an open file-like object.
   When ``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'
