public static function image()
 {
     WPI_Log::get_instance()->log('wpi api upload image : ' . json_encode($_FILES));
     $server_now = new WPI_Server();
     $dir = wp_upload_dir();
     $img_types = array('image/gif', 'image/pjpeg', 'image/jpeg', 'image/png');
     if (!in_array($_FILES['img']['type'], $img_types)) {
         $server_now->response_failure('type not allowed ');
     } else {
         $save_to = $dir['path'] . '/' . $_FILES['img']['name'];
         if (file_exists($save_to)) {
             $server_now->response_failure('file has exist !');
         } else {
             $result = move_uploaded_file($_FILES['img']['tmp_name'], $save_to);
             $server_now->response_success_with_data('image uploaded !', '"' . $dir['url'] . '/' . $_FILES['img']['name'] . '"');
         }
     }
 }