Images: blanks.pngs create ?

I created divs in my css that reference images – then in the php file I added that div that referenced a blank image but with the class made in my css. This works in Firefox but it creates a blue ? in Safari. Apple says it’s from the blanks….here’s the css and the div.

div#photo.main { background-image:url('images/photo-main.jpg'); width: 480px; height: 334px; margin: 0px 15px 0px 0px; padding: 0px; }

<div id="photo" class="main"><img src="images/spacer.png"/></div>