Here is an example on how to obscure email addresse (or other tekst) using http://drupal.org/project/signwriter in a formatter. You can use it on the cck field overview as a formatter (or in display suite).
<?php
//cck formatters
/**
* Implementation of hook_field_formatter_info(),.
*/
function your_module_field_formatter_info() {
return array(
'text_as_image' => array(?>
