function sar_attachment_redirect() {
    global $post;
    if ( is_attachment() && isset($post->post_parent) && is_numeric($post->post_parent) && ($post->post_parent != 0) ) {
        wp_redirect(get_permalink($post->post_parent), 301); // permanent redirect to post/page where image or document was uploaded
        exit;
    } elseif ( is_attachment() && isset($post->post_parent) && is_numeric($post->post_parent) && ($post->post_parent < 1) ) {   // for some reason it doesnt works checking for 0, so checking lower than 1 instead...
        wp_redirect(get_bloginfo('wpurl'), 302); // temp redirect to home for image or document not associated to any post/page
        exit;
}
}
add_action('template_redirect', 'sar_attachment_redirect',1);