Adding Images to XML and displaying with PHP

After hours I finally managed to get this Simple XML working now. I now want to enchance and was wondering if anyone knows how to add image links to the XML and display it with PHP.

XML File

<?xml version=“1.0” encoding=“utf-8”?>
<library>
<shelf id=“fiction”>
<book>
<title>Of Mice and Men</title>
<author>John Steinbeck</author>
<desc>Whats this</desc>
</book>
<book>
<title>Harry Potter and the Philosopher’s Stone</title>
<author>J.K. Rowling</author>
<desc>Whats that</desc>
</book>
</shelf>
</library>

PHP File

<?php
$library = simplexml_load_file(‘library.xml’);
foreach ($library->shelf as $shelf) {
printf("Shelf %s
", $shelf[‘id’]);
foreach ($shelf->book as $book) {
printf("Title: %s
", $book->title);
printf("Author: %s
", $book->author);
printf("Description: %s
", $book->desc);
}
}
?>

I want to add a image field to the XML for each of the books and display it with PHP.