title: PIL - saving image as .jpg not working
body: <p>I'm trying to overwrite save() method of the model to resize images. Every format works, except when saving a .jpg image. It's not saving images with .jpg extension.</p>
  
  <p>I read the Pillow documentation and there's no JPG format.</p>
  
  <pre><code>class Business(models.Model):
  photo = models.ImageField(_('photo'), storage=OverwriteStorage(),
                            upload_to=image_upload_to, blank=True, null=True)
  
  
  def save(self, **kwargs):
      """
      Changing dimensions of images if they are to big.
      Set max height or width to 800px depending on the image is portrait or landscape.
      """
      # Opening the uploaded image
      im = Image.open(self.photo)
      print(im)
      output = BytesIO()
      # set the max width or height
      im.thumbnail((800, 800))
      # find the ext of the file
      ext = self.photo.name.split('.')[1].upper()
  
      if ext in {'JPEG', 'PNG', 'GIF', 'TIFF'}:
          # after modifications, save it to the output
          im.save(output, format=ext, quality=100)
          output.seek(0)
          # change the imagefield value to be the newley modifed image value
          self.photo = InMemoryUploadedFile(output, 'ImageField', "%s.jpg" % self.photo.name.split('.')[0],
                                            'image/jpeg', sys.getsizeof(output), None)
          super(User, self).save()
  </code></pre>
  
  <p>I don't know what I am missing here.</p>
  
  <p>And what's the best way to do this on a custom User model. Using a signal, overwriting ImageField or ...</p>
  
  <p>Any help is appreciated :)</p>