Okay, let's say you have something like this:
<span class="image" style="background-image: url('http://www.example.com/images/image1.png')"></span>
Every CSS tutorial I've ever read has covered the concept of using a background color after the background-image code, which of course takes the place of the image when one is unavailable, but...
How do you specify a backup background-image - one that should be displayed if the image referenced is unavailable? If there's no CSS trick for this, maybe JavaScript could handle it?