$news_txt    = preg_replace('/\[img id\=(.*?)\]/is', $this->Img2Out("$1"), $news_txt);

!class this

function Img2Out($img_id){ 
  $this->DB("table");
  $img_res = mysql_query("SELECT * FROM news_img WHERE img_id='$img_id'");
  $ir = mysql_fetch_array($img_res);
  if(@mysql_num_rows($img_res) == 1) {
    return "<img src=\"/news/".$img_name."\" alt=\"\" />"; 
  }
  else { return $img_id; }
}