Django thumbnails for admin

models.py

def resize_images(image_field):
    pathname, filename = path.split(image_field.path)
    img_file = Image.open(image_field.path)

    # Convert to RGB
    if img_file.mode not in ('L', 'RGB'):
        img_file = img_file.convert('RGB')

    # Save a thumbnail file for each of the given dimensions,
    # prefixed with med_, small_ etc
    IMAGE_SIZES = {
        'med_': (250, 250),
        'small_': (100, 100)
    }

    # each of which corresponds to an ImageField of the same name
    for field_name, size in IMAGE_SIZES.iteritems():
        working = img_file.copy()
        working.thumbnail(size, Image.ANTIALIAS)
        working.save(pathname + '/' + field_name + filename, working.format, quality=70)
        
class Foo(models.Model):

    image = models.ImageField('Image', upload_to='images/')

    def save(self):
        super(Foo, self).save()
        resize_images(image_field=self.image)