email contact form -- replace Submit button with image?

[dpajevic]

V. 1.2.1 -- Does anyone know how to replace the html Submit button with a custom image? I've found this code in cnt23.article.inc.php, line 627, but how do you access it?

$form_field .= '<input type="image" name="'.$form_name.'" id="'.$form_name.'" ';

Or maybe there is a way in the "article content — email contact form" page?

Thanks for your help.