*
		 * add_filter(
		 *     'smush_cdn_custom_uploads_dir',
		 *     function( $uploads ) {
		 *         $uploads['baseurl'] = 'https://example.com/media';
		 *         return $uploads;
		 *     }
		 * );
		 */
		$uploads = apply_filters( 'smush_cdn_custom_uploads_dir', wp_get_upload_dir() );
		// Check if the src is within custom uploads directory.
		$uploads = isset( $uploads['baseurl'] ) ? false !== strpos( $src, $uploads['baseurl'] ) : true;

		if ( ( false === strpos( $src, content_url() ) && ! $uploads ) || ( is_multisite() && $mapped_domain && false === strpos( $src, $mapped_domain ) ) ) {
			return false;
		}

		return $src;
	}

	/**
	 * Support for domain mapping plugin.
	 *
	 * @since 3.1.1
	 */
	private function check_mapped_domain() {
		if ( ! is_multisite() ) {
			return false;
		}

		if ( ! defined( 'DOMAINMAP_BASEFILE' ) ) {
			return false;
		}

		$domain = wp_cache_get( 'smush_mapped_site_domain', 'smush' );

		if ( ! $domain ) {
			global $wpdb;

			$domain = $wpdb->get_var(
				$wpdb->prepare(
					"SELECT domain FROM {$wpdb->base_prefix}domain_mapping WHERE blog_id = %d ORDER BY id LIMIT 1",
					get_current_blog_id()
				)
			); // Db call ok.

			if ( null !== $domain ) {
				wp_cache_add( 'smush_mapped_site_domain', $domain, 'smush' );
			}
		}

		return $domain;
	}

	/**
	 * Init the page parser.
	 */
	private function init_parser() {
		$background_images = $this->settings->get( 'background_images' );

		if ( $background_images ) {
			$this->parser->enable( 'background_images' );
		}

		$this->parser->enable( 'cdn' );
	}

	/**
	 * Try to get the image dimensions from a local file.
	 *
	 * @since 3.4.0
	 * @param string $url  Image URL.
	 *
	 * @return array|false
	 */
	private function get_image_size( $url ) {
		if ( $this->site_url !== $this->home_url ) {
			$url = str_replace( $this->site_url, $this->home_url, $url );
		}

		$path = wp_make_link_relative( $url );
		$path = wp_normalize_path( ABSPATH . $path );

		if ( ! file_exists( $path ) ) {
			return false;
		}

		return getimagesize( $path );
	}

}