Inventory_Presser_Plugin::change_attachment_urls( string $url, int $post_id = null )

	public function change_attachment_urls( $url, $post_id = null ) {
		if ( empty( $post_id ) ) {
			$post_id = attachment_url_to_postid( $url );
		}

		if ( INVP::POST_TYPE !== get_post_type( wp_get_post_parent_id( $post_id ) ) ) {
			return $url;
		}

		// Is the URL pointing to a file with an image mime type?
		$file      = get_attached_file( $post_id );
		$mime_type = wp_get_image_mime( $file );
		if ( $mime_type && 'image' !== substr( $mime_type, 0, 5 ) ) {
			return $url;
		}

		// Add a querystring that contains this photo's hash.
		$hash = INVP::get_meta( 'hash', $post_id );
		if ( empty( $hash ) ) {
			return $url;
		}

		$parsed = wp_parse_url( $url );
		return $url . ( empty( $parsed['query'] ) ? '?' : '&' ) . $hash;
	}