public function makeThumbnailsForBookCover() {

		$post = $this->getMetaPost();
		if ( $post ) {

			$pb_cover_image = get_post_meta( $post->ID, 'pb_cover_image', true );
			if ( $pb_cover_image && ! \Pressbooks\Image\is_default_cover( $pb_cover_image ) ) {

				$path = \Pressbooks\Utility\get_media_path( $pb_cover_image );
				$type = wp_check_filetype( $path );
				$type = $type['type'];

				// Insert new image, create thumbnails
				$args = [
					'post_mime_type' => $type,
					'post_title' => __( 'Cover Image', 'pressbooks' ),
					'post_content' => '',
					'post_status' => 'inherit',
				];

				include_once( ABSPATH . 'wp-admin/includes/image.php' );
				$id = wp_insert_attachment( $args, $path, $post->ID );
				wp_update_attachment_metadata( $id, wp_generate_attachment_metadata( $id, $path ) );
				Book::deleteBookObjectCache();
			}
		}
	}