ASCII font patterns appear in Search engine keywords and can be pattern matched - suggest randomization

Love the ASCII CAPTCHA and have been using it on my personal site for a while. Whilst looking at site analytics I noticed that I was getting keyword assignments from the ASCII art because of high occurrences of "d88p" and "y88b". I am using the "colossal" font which uses these strings frequently. To overcome this problem I added a string randomizer that replaces the '8' character, that is mainly used as a filler in this font, with a random character of roughly equal visual weight and shape.

I have attached a comparison image that show the original font with a randomize version below it. Here's the font specific code I used. It could be modified to work with other fonts. Just thought I would share it.

function randomize_eight($font) {
  if (is_array($font) && count($font)) {
    foreach ($font as $x => $f) {
      if (is_array($f) && count($f)) {
        foreach($f as $y => $l) {     
          $font[$x][$y] = preg_replace_callback('|8|', randomize_digit, $l);
        }
      }
    }
  }
  return $font;
}

function randomize_digit() {
  $source = '@895ESHM';
  $max = strlen($source) -1;
  return substr($source, rand(0,$max), 1);
}

// $font = randomize_eight(ASCII_art_captcha_font_colossal());

As a by-product this also strengthens the ASCII capture because the fonts are much harder to pattern match.