Serving images from outside of document root

The most common way is an Alias :

Alias /data/ /wherever/your/data/are/

Another way (say if you can't set an alias...) would be to use a script as the image source eg:

<img src="image.php?img=myImage.jpg" />

image.php would be similar to:

<?php
  header('Content-Type: image/jpg');
  readfile("../img/" . $_GET['img']);
?>

Of course you'd need to extend the script to filter $_GET['img'], as well as detect and set the right content type. Your script could even resize the image according to other parameters passed in the query string.