imghdr is deprecated and slated for removal in Python 3.13

[domdfcoding]

Describe the bug

The imghdr module is deprecated in Python 3.11 by PEP 594 and is slated for removal in Python 3.13.

imghdr is used here to guess image mimetypes:

sphinx/sphinx/util/images.py

Lines 50 to 55 in 31eba1a

	def guess_mimetype_for_stream(stream: IO, default: Optional[str] = None) -> Optional[str]:
	imgtype = imghdr.what(stream)
	if imgtype:
	return 'image/' + imgtype
	else:
	return default

The imghdr code is not very large (see here). It could either be vendored by Sphinx or pulled out to a package on PyPI if there's no alternative.

Python version

Python 3.11.0.beta1

[tk0miya]

Now we're using the imagesize package to obtain the image file size. It's better to extend it to detect the type of image.
https://pypi.org/project/imagesize/

And it's much better to use the Pillow package as a fallback when the imagesize can't detect the type.

[trevorbaca]

Hi,

With the public release of Python 3.11, the deprecation warning for imghdr is now showing up.

Any idea when imghdr might be removed?

Thanks!