here is what you need to do.
1) create a folder in 'wordpress/wp-content' called 'hdr_images' (actually you can call it what ever you want)
2) find the PAGE ID for each page (go to dashboard->pages->edit and edit a page in question. Look at the browser's address bar, you will see something like
HTML Code:
http://yourdomain.com/wordpress/wp-admin/page.php?action=edit&post=2
the number at the end is the PAGE ID
3) add a CSS insert for each page. The format will be like this
HTML Code:
body.page-id-2 div#imagecontainer {
background-image: url('http://yourdomain.com/wordpress/wp-content/hdr_images/page_2.jpg') !important;
}
create a CSS insert for each page you want a single image to show up on.