initフックとget-value を使用してプラグインを作成することもできます$_GET[ 'file' ];。ユーザーがこのget-valueを持っている場合、ファイルのアクセス権をチェックする関数にジャンプします。たとえば、メタボックスのチェックボックスを使用します。
add_action( 'init', 'fb_init' );
function fb_init() {
    // this in a function for init-hook
    if ( '' != $_GET[ 'file' ] ) {
        fb_get_file( $_GET[ 'file' ] );
    }
}
関数get_file()
function fb_get_file( $file ) {
    $upload     = wp_upload_dir();
    $the_file   = $file; 
    $file       = $upload[ 'basedir' ] . '/' . $file;
    if ( !is_file( $file ) ) {
        status_header( 404 );
        die( '404 — File not found.' );
    }
    else {
        $image = get_posts( array( 'post_type' => 'attachment', 'meta_query' => array( array( 'key' => '_wp_attached_file', 'value' => $the_file ) ) ) );
        if ( 0 < count( $image ) && 0 < $image[0] -> post_parent ) { // attachment found and parent available
            if ( post_password_required( $image[0] -> post_parent ) ) { // password for the post is not available
                wp_die( get_the_password_form() );// show the password form 
            }
            $status = get_post_meta( $image[0] -> post_parent, '_inpsyde_protect_content', true );
            if ( 1 == $status &&  !is_user_logged_in() ) {
                wp_redirect( wp_login_url( $upload[ 'baseurl' ] . '/' . $the_file ) );
                die();
            }
        }
        else {
            // not a normal attachment check for thumbnail
            $filename   = pathinfo( $the_file );
            $images     = get_posts( array( 'post_type' => 'attachment', 'meta_query' => array( array( 'key' => '_wp_attachment_metadata', 'compare' => 'LIKE', 'value' => $filename[ 'filename' ] . '.' . $filename[ 'extension' ] ) ) ) );
            if ( 0 < count( $images ) ) {
                foreach ( $images as $SINGLEimage ) {
                    $meta = wp_get_attachment_metadata( $SINGLEimage -> ID );
                    if ( 0 < count( $meta[ 'sizes' ] ) ) {
                        $filepath   = pathinfo( $meta[ 'file' ] );
                        if ( $filepath[ 'dirname' ] == $filename[ 'dirname' ] ) {// current path of the thumbnail
                            foreach ( $meta[ 'sizes' ] as $SINGLEsize ) {
                                if ( $filename[ 'filename' ] . '.' . $filename[ 'extension' ] == $SINGLEsize[ 'file' ] ) {
                                    if ( post_password_required( $SINGLEimage -> post_parent ) ) { // password for the post is not available
                                        wp_die( get_the_password_form() );// show the password form 
                                    }
                                    die('dD');
                                    $status = get_post_meta( $SINGLEimage -> post_parent, '_inpsyde_protect_content', true );
                                    if ( 1 == $status &&  !is_user_logged_in() ) {
                                        wp_redirect( wp_login_url( $upload[ 'baseurl' ] . '/' . $the_file ) );
                                        die();
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }
    $mime       = wp_check_filetype( $file );
    if( false === $mime[ 'type' ] && function_exists( 'mime_content_type' ) )
        $mime[ 'type' ] = mime_content_type( $file );
    if( $mime[ 'type' ] )
        $mimetype = $mime[ 'type' ];
    else
        $mimetype = 'image/' . substr( $file, strrpos( $file, '.' ) + 1 );
    header( 'Content-type: ' . $mimetype ); // always send this
    if ( false === strpos( $_SERVER['SERVER_SOFTWARE'], 'Microsoft-IIS' ) )
        header( 'Content-Length: ' . filesize( $file ) );
    $last_modified = gmdate( 'D, d M Y H:i:s', filemtime( $file ) );
    $etag = '"' . md5( $last_modified ) . '"';
    header( "Last-Modified: $last_modified GMT" );
    header( 'ETag: ' . $etag );
    header( 'Expires: ' . gmdate( 'D, d M Y H:i:s', time() + 100000000 ) . ' GMT' );
    // Support for Conditional GET
    $client_etag = isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) ? stripslashes( $_SERVER['HTTP_IF_NONE_MATCH'] ) : false;
    if( ! isset( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) )
        $_SERVER['HTTP_IF_MODIFIED_SINCE'] = false;
    $client_last_modified = trim( $_SERVER['HTTP_IF_MODIFIED_SINCE'] );
    // If string is empty, return 0. If not, attempt to parse into a timestamp
    $client_modified_timestamp = $client_last_modified ? strtotime( $client_last_modified ) : 0;
    // Make a timestamp for our most recent modification...
    $modified_timestamp = strtotime($last_modified);
    if ( ( $client_last_modified && $client_etag )
        ? ( ( $client_modified_timestamp >= $modified_timestamp) && ( $client_etag == $etag ) )
        : ( ( $client_modified_timestamp >= $modified_timestamp) || ( $client_etag == $etag ) )
        ) {
        status_header( 304 );
        exit;
    }
    // If we made it this far, just serve the file
    readfile( $file );
    die();
}
フック経由でファイルのカスタムURLを追加することもできます generate_rewrite_rules
add_filter( 'generate_rewrite_rules', 'fb_generate_rewrite_rules' );
function fb_generate_rewrite_rules( $wprewrite ) {
        $upload = wp_upload_dir();
        $path = str_replace( site_url( '/' ), '', $upload[ 'baseurl' ] );
        $wprewrite -> non_wp_rules = array( $path . '/(.*)' => 'index.php?file=$1' );
        return $wprewrite;
}