To quickly build a human-readable random string for a captcha per example :
  

  

  <?php
  

  

  function random($length = 8)
  

  {
  

  $chars = 'bcdfghjklmnprstvwxzaeiou';
  

  

  for ($p = 0; $p < $length; $p++)
  

  {
  

  $result .= ($p%2) ? $chars[mt_rand(19, 23)] : $chars[mt_rand(0, 18)];
  

  }
  

  

  return $result;
  

  }
  

  

  ?>
  

  

  Note that I have removed q and y from $chars to avoid readability problems.