Javascript change background image of div

My javascript seems to work Ok with the text changing fine and the background image seems to be changed (it shows me the correct path in the alert) but the image does not show. Help!

<script type="text/javascript">
        function changeDivImage(ImageURL,ImageText) {
            document.getElementById('desc').innerHTML = ImageText;
            document.getElementById('headerimage').style.backgroundImage = 'url(' + ImageURL + ')';
            alert( document.getElementById('headerimage').style.backgroundImage)
        }
 
    </script>
 
CALLED FROM
 
                    <ul>
                        <li id="liOne" class="one"><a href="#" onclick="javascript:changeDivImage('../images/headerbantham.jpg','Bantham,Devon')"><img src="images/1x1.gif" height="20px" width="20px" alt="" style="padding:0; margin:0;" /></a></li>
                        <li id="liTwo" class="two"><a href="#" onclick="javascript:changeDivImage('../images/headertorquay.jpg','Torquay,Devon')"><img src="images/1x1.gif" height="20px" width="20px" alt="" /></a></li>
</ul>

Select allOpen in new window