Treat MPO with unknown header as base JPEG file

PIL/JpegImagePlugin.py

@@ -37,6 +37,7 @@ __version__ = "0.6"
 import array
 import struct
 import io
+import warnings
 from struct import unpack
 from PIL import Image, ImageFile, TiffImagePlugin, _binary
 from PIL.JpegPresets import presets
@@ -713,8 +714,8 @@ def _save_cjpeg(im, fp, filename):
 # Factory for making JPEG and MPO instances
 def jpeg_factory(fp=None, filename=None):
     im = JpegImageFile(fp, filename)
-    mpheader = im._getmp()
     try:
+        mpheader = im._getmp()
         if mpheader[45057] > 1:
             # It's actually an MPO
             from .MpoImagePlugin import MpoImageFile
@@ -722,6 +723,10 @@ def jpeg_factory(fp=None, filename=None):
     except (TypeError, IndexError):
         # It is really a JPEG
         pass
+    except SyntaxError:
+        warnings.warn("Image appears to be a malformed MPO file, it will be "
+                      "interpreted as a base JPEG file")
+        pass
     return im
 
 

Tests/test_file_jpeg.py

@@ -353,6 +353,17 @@ class TestFileJpeg(PillowTestCase):
         reloaded.save(f, quality='keep', progressive=True)
         reloaded.save(f, quality='keep', optimize=True)
 
+    def test_bad_mpo_header(self):
+        """ Treat unknown MPO as JPEG """
+        # Arrange
+
+        # Act
+        # Shouldn't raise error
+        im = Image.open("Tests/images/sugarshack_bad_mpo_header.jpg")
+
+        # Assert
+        self.assertEqual(im.format, "JPEG")
+
 
 if __name__ == '__main__':
     unittest.main()