Hey,
You can update email_registrationaccepted.php. The code to show the pilot id is this:
<?php echo PilotData::GetPilotCode($pilot->code, $pilot->pilotid)?>
Regarding the image code, you can use html on this file. The exact format for the image is this:
<img src="wrongname.gif" alt="HTML5 Icon" />
There are many html tags you can use. http://www.w3schools.com/html/