realagenda on "Adding different image to each page site"

How do I find the page-id of each of the pages in my site so I can use the below code

body.page-id-2689 h1.title {background-image:url("IMAGE-URL"); text-indent:-999em; height:###px; width:###px; padding-bottom:0;}

to add a different image to each page in the content area where the pages now have the red titles?

Thank you, greatly appreciate your help.