public static function generateAvatarMarkup($user_id)
    {
        $filetypes = ['jpg', 'gif', 'png'];
        $avatar_markup = '';

        foreach ($filetypes as $cur_type) {
            $path = ForumSettings::get('o_avatars_dir') . '/' . $user_id . '.' . $cur_type;

            if (file_exists(ForumEnv::get('WEB_ROOT') . $path) &&
                $img_size = getimagesize(ForumEnv::get('WEB_ROOT') . $path)
            ) {
                $avatar_markup = '<img class="avatar" src="' .
                    \RunBB\Core\Utils::escape(Container::get('url')->base() . $path . '?m=' .
                        filemtime(ForumEnv::get('WEB_ROOT') . $path)) . '" ' . $img_size[3] . ' alt="" />';
                break;
            }
        }

        return $avatar_markup;
    }