--- contrib/python/future/py3/future/backports/email/mime/image.py	(index)
+++ contrib/python/future/py3/future/backports/email/mime/image.py	(working tree)
@@ -9,8 +9,6 @@ from __future__ import absolute_import
 
 __all__ = ['MIMEImage']
 
-import imghdr
-
 from future.backports.email import encoders
 from future.backports.email.mime.nonmultipart import MIMENonMultipart
 
@@ -40,9 +38,118 @@ class MIMEImage(MIMENonMultipart):
         header.
         """
         if _subtype is None:
-            _subtype = imghdr.what(None, _imagedata)
+            _subtype = _what(_imagedata)
         if _subtype is None:
             raise TypeError('Could not guess image MIME subtype')
         MIMENonMultipart.__init__(self, 'image', _subtype, **_params)
         self.set_payload(_imagedata)
         _encoder(self)
+
+
+_rules = []
+
+
+# Originally from the imghdr module.
+def _what(data):
+    for rule in _rules:
+        if res := rule(data):
+            return res
+    else:
+        return None
+
+
+def rule(rulefunc):
+    _rules.append(rulefunc)
+    return rulefunc
+
+
+@rule
+def _jpeg(h):
+    """JPEG data with JFIF or Exif markers; and raw JPEG"""
+    if h[6:10] in (b'JFIF', b'Exif'):
+        return 'jpeg'
+    elif h[:4] == b'\xff\xd8\xff\xdb':
+        return 'jpeg'
+
+
+@rule
+def _png(h):
+    if h.startswith(b'\211PNG\r\n\032\n'):
+        return 'png'
+
+
+@rule
+def _gif(h):
+    """GIF ('87 and '89 variants)"""
+    if h[:6] in (b'GIF87a', b'GIF89a'):
+        return 'gif'
+
+
+@rule
+def _tiff(h):
+    """TIFF (can be in Motorola or Intel byte order)"""
+    if h[:2] in (b'MM', b'II'):
+        return 'tiff'
+
+
+@rule
+def _rgb(h):
+    """SGI image library"""
+    if h.startswith(b'\001\332'):
+        return 'rgb'
+
+
+@rule
+def _pbm(h):
+    """PBM (portable bitmap)"""
+    if len(h) >= 3 and \
+            h[0] == ord(b'P') and h[1] in b'14' and h[2] in b' \t\n\r':
+        return 'pbm'
+
+
+@rule
+def _pgm(h):
+    """PGM (portable graymap)"""
+    if len(h) >= 3 and \
+            h[0] == ord(b'P') and h[1] in b'25' and h[2] in b' \t\n\r':
+        return 'pgm'
+
+
+@rule
+def _ppm(h):
+    """PPM (portable pixmap)"""
+    if len(h) >= 3 and \
+            h[0] == ord(b'P') and h[1] in b'36' and h[2] in b' \t\n\r':
+        return 'ppm'
+
+
+@rule
+def _rast(h):
+    """Sun raster file"""
+    if h.startswith(b'\x59\xA6\x6A\x95'):
+        return 'rast'
+
+
+@rule
+def _xbm(h):
+    """X bitmap (X10 or X11)"""
+    if h.startswith(b'#define '):
+        return 'xbm'
+
+
+@rule
+def _bmp(h):
+    if h.startswith(b'BM'):
+        return 'bmp'
+
+
+@rule
+def _webp(h):
+    if h.startswith(b'RIFF') and h[8:12] == b'WEBP':
+        return 'webp'
+
+
+@rule
+def _exr(h):
+    if h.startswith(b'\x76\x2f\x31\x01'):
+        return 'exr'