Someone

$completo = 0;
while ( $completo < $total ) {
  preg_match("/<img src=[^%]/i", $html_body, $imagen);
  list($a, $b) = explode("=", $imagen[0]);
  switch ($b) {
    case "\"":
      $tag = "<img src=%\"".$base_url;
      break;
    default:
      $tag = "<img src=%".$base_url.$b;
  }
  $count = 0;
  $nuevo = preg_replace("/<img src=[^%]/i", $tag, $html_body);
  $completo++;
}