21.8. "imghdr" — Determine the type of an image
***********************************************

**Source code:** Lib/imghdr.py

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

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           |
+--------------+-------------------------------------+

New in version 2.5: Exif detection.

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('bass.gif')
   'gif'
