public static function add_thumbnail_support() {

		// Ensure theme support exists for LifterLMS post types.
		if ( ! current_theme_supports( 'post-thumbnails' ) ) {
			add_theme_support( 'post-thumbnails' );
		}

		$thumbnail_post_types = array(
			'course',
			'lesson',
			'llms_membership',
		);

		foreach ( $thumbnail_post_types as $p ) {

			add_post_type_support( $p, 'thumbnail' );

		}

		add_image_size( 'llms_notification_icon', 64, 64, true );

	}