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21.4. 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

New in version 2.5: Exif detection.

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


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.


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