I’ll assume you are doing this within a cascading style sheet with something like this:
body {background-image: url(images/photo.gif) no-repeat top left;}
Make sure your path to the image is correct. The path you have places the images folder immediately off the root so it would be located at:
<a href="http://www.yoursite.com/images/photo.gif">http://www.yoursite.com/images/photo.gif</a>
And if you were to type the above directly into your address bar on your browser, do you get the image?
Or you can try it like this:
{background: url(images/photo.gif) no-repeat top left;}