I think you would be able to do something similar to this notion. Basically, for each page of your web site that you would like a BG image, you will create a corresponding ID in your style sheet. For instance, if you have three pages to your site, you would create three body ID's, each with a different style (bg img).
So, the first thing you would do is create the body ID's (in your stylesheet) to match the pages you have on your site where you want bg-images, and style with appropriate image. (in this example, three pages: main, about, contact):
<style type="text/css">
body#main { background: #fff url(images/bg/main.gif) no-repeat; }
body#about { background: #fff url(images/bg/about.gif) no-repeat; }
body#contact { background: #fff url(images/bg/contact.gif) no-repeat; }
/* etc... */
</style>
Save your CSS stylesheet.
Next is using PHP to capture the page you are on, so that the corresponding bodyID can be echoed out in the HTML, and the corresponding style will be attributed to the page.
When you have the page variable defined (probably using the $page = $_GET['page']; value), you can use that to echo the complete opening body tag, with the bodyID:
<?php
// put this in place of your body tag
if ($page == "MAIN"){
$bodyID = 'main';
}
elseif ($page == "ABOUT"){
$bodyID = 'about';
}
else {
$bodyID = 'contact';
}
echo '<body id="'. $bodyID . '">' . "\n";
?>
I got the idea from A List Apart's old web site, where they had the navigation change to highlight the page the viewer was on. I thought, if you could do that with the way a link was styled, why couldn't you do this with BG images?