from PIL import Image

class Photo(models.Model):
    source = models.ImageField(upload_to='images')

    def save(self, size=(400, 300)):
        """
        Save Photo after ensuring it is not blank.  Resize as needed.
        """

        if not self.id and not self.source:
            return

        super(Photo, self).save()

        filename = self.get_source_filename()
        image = Image.open(filename)
    
        image.thumbnail(size, Image.ANTIALIAS)
        image.save(filename)