TS part:
includeLibs.testMD5 = Fileadmin/makeMD5.php
page.10.marks.CONTENT = USER
page.10.marks.CONTENT {
  userFunc = user_makeMD5->main
  value = TestString
  color = #11FAAA
}

PHP File:
<?php
  class user_makeMD5 {
    var $cObj;
    function main($content,$conf){
      $content .= '<span style="olor:' .$conf["color"]'.'"
                  >'.$conf["value"].' as md5
                  '.md5($conf["value"]).'</span>';
    }
  }
?>