Stuff

<pre>
<?php

$domains = array("google.com", "www.google.com");

# HTML copied from a parsed post in the database
$post = <<<EOF
internal - <img src="http://www.google.com/logo.gif" border="0" class="linked-image" /><br />external - <img src="http://engadget.com/path/to/test.gif" border="0" class="linked-image" /><br />external - <img src="https://www.example.com/a/b/c.png" border="0" class="linked-image" /><br />internal -<br />
EOF;

  $domains = implode("|", array_map("preg_quote", $domains));
  preg_match_all("/<img src=\"((?:ftp|http)s?:\/\/(?!$domains)(.+?))\"/si", $post, $matches, PREG_SET_ORDER);
  print_r($matches);
?>