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():
SGI ImgLib Files
GIF 87a and 89a Files
Portable Bitmap Files
Portable Graymap Files
Portable Pixmap Files
Sun Raster Files
X Bitmap Files
JPEG data in JFIF format
Portable Network Graphics
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.