Normalize name and size images in Django (and adding thumbnails)

I wanted to assign an image to every element in a model. I wanted them to have a thumbnail, and to have normalized sizes and names. And of course, I want my application to do everything automatically.

The best method I've found is next, modifying models.py (note that PIL must be installed):

def rename_image(src, field, id):
    file_ext = os.path.splitext(src)[1].lower().replace('jpg', 'jpeg')
    dst = 'img/uploaded/work_%s/%s_%s%s' % (field, field, id, file_ext)
    return dst



def resize_image(src, dst, size):
    from PIL import Image
    image = Image.open(src)
    image.thumbnail(size, Image.ANTIALIAS)
    image.save('%s%s' % (settings.MEDIA_ROOT, dst))
    return dst



class MyModel(models.Model):
    image = models.ImageField(upload_to='img/uploaded/work_image', verbose_name=_('imagen'))
    thumbnail = models.ImageField(editable=False, upload_to='img/uploaded/work_thumbnail')
    [...]



    def save(self):
        super(MyModel, self).save()
        if self.image != rename_image(self.image, 'image', self.id):
            original_filename = self.get_image_filename()
            self.thumbnail = resize_image(original_filename, rename_image(original_filename, 'thumbnail', self.id), [100, 75])
            self.image = resize_image(original_filename, rename_image(original_filename, 'image', self.id), [640, 480])
            if os.path.exists(original_filename):
                os.remove(original_filename)
            super(MyModel, self).save()