Remove pre-Django 1.8 code from check_image_file_format

wagtail/wagtailimages/fields.py

@@ -7,7 +7,6 @@ from django.core.exceptions import ValidationError
 from django.forms.fields import ImageField
 from django.template.defaultfilters import filesizeformat
 from django.utils.translation import ugettext_lazy as _
-from PIL import Image
 
 ALLOWED_EXTENSIONS = ['gif', 'jpg', 'jpeg', 'png']
 SUPPORTED_FORMATS_TEXT = _("GIF, JPEG, PNG")
@@ -60,31 +59,11 @@ class WagtailImageField(ImageField):
         if extension not in ALLOWED_EXTENSIONS:
             raise ValidationError(self.error_messages['invalid_image'], code='invalid_image')
 
-        if hasattr(f, 'image'):
-            # Django 1.8 annotates the file object with the PIL image
-            image = f.image
-        elif not f.closed:
-            # Open image file
-            file_position = f.tell()
-            f.seek(0)
-
-            try:
-                image = Image.open(f)
-            except IOError:
-                # Uploaded file is not even an image file (or corrupted)
-                raise ValidationError(self.error_messages['invalid_image_known_format'],
-                                      code='invalid_image_known_format')
-
-            f.seek(file_position)
-        else:
-            # Couldn't get the PIL image, skip checking the internal file format
-            return
-
         image_format = extension.upper()
         if image_format == 'JPG':
             image_format = 'JPEG'
 
-        internal_image_format = image.format.upper()
+        internal_image_format = f.image.format.upper()
         if internal_image_format == 'MPO':
             internal_image_format = 'JPEG'