def get_thumbnails(self, *args, **kwargs):
        """
        Return an iterator which returns ThumbnailFile instances.
        """
        # First, delete any related thumbnails.
        source_cache = self.get_source_cache()
        if source_cache:
            thumbnail_storage_hash = utils.get_storage_hash(
                self.thumbnail_storage)
            for thumbnail_cache in source_cache.thumbnails.all():
                # Only iterate files which are stored using the current
                # thumbnail storage.
                if thumbnail_cache.storage_hash == thumbnail_storage_hash:
                    yield ThumbnailFile(name=thumbnail_cache.name,
                                        storage=self.thumbnail_storage)
Return an iterator which returns ThumbnailFile instances.