bpo-44539: Support recognizing JPEG files without JFIF or Exif markers

Lib/imghdr.py

@@ -35,9 +35,11 @@ def what(file, h=None):
 tests = []
 
 def test_jpeg(h, f):
-    """JPEG data in JFIF or Exif format"""
+    """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'
 
 tests.append(test_jpeg)
 

Lib/test/test_imghdr.py

@@ -16,6 +16,7 @@
     ('python.pgm', 'pgm'),
     ('python.pbm', 'pbm'),
     ('python.jpg', 'jpeg'),
+    ('python-raw.jpg', 'jpeg'),  # raw JPEG without JFIF/EXIF markers
     ('python.ras', 'rast'),
     ('python.sgi', 'rgb'),
     ('python.tiff', 'tiff'),

Misc/NEWS.d/next/Library/2021-06-30-11-34-35.bpo-44539.nP0Xi4.rst

@@ -0,0 +1 @@
+Added support for recognizing JPEG files without JFIF or Exif markers.