public static function crop($image_url, $args, $size_name = '')
 {
     if (!function_exists('wpthumb')) {
         return $image_url;
     }
     $thumb = new self();
     $thumb->image_url = $image_url;
     $thumb->args = $args;
     $thumb->size_name = $size_name;
     $thumb->prepare_watermark();
     return $thumb->get_src();
 }