Do not index attachment pages in WordPress

hip_attachments_noindex.php

<?php
/*
Plugin Name:  Hippies attachments noindex 
Plugin URI:   
Description:  Do not index attachment pages and set default image link type to "none" on plugin activation.
Version:      1
Author:       Hippies
Author URI:   http://hippies.se/
*/
add_action( 'wp_head', 'hip_attachments_noindex_wp_head' );
function hip_attachments_noindex_wp_head() {
    if( is_attachment() ) {
        echo '<meta name="robots" content="noindex, follow">';
    }
}
function hip_attachments_noindex_activate() {
    update_option( 'image_default_link_type', 'none' );
}
register_activation_hook( __FILE__, 'hip_attachments_noindex_activate' );