imghdr — Determine the type of an image

Source code: Lib/

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=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.

Changed in version 3.6: Accepts a path-like object.

The following image types are recognized, as listed below with the return value from what():


Image format


SGI ImgLib Files


GIF 87a and 89a Files


Portable Bitmap Files


Portable Graymap Files


Portable Pixmap Files


TIFF Files


Sun Raster Files


X Bitmap Files


JPEG data in JFIF or Exif formats


BMP files


Portable Network Graphics


WebP files


OpenEXR Files

New in version 3.5: The exr and webp formats were added.

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('bass.gif')