<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Example</title>
<style type="text/css">
#spoiler{background:url('1.jpg');margin:0 auto;height:200px;width:200px;}
</style>
</head>
<body>
<div id="spoiler" onclick="show(this)">Спойлер)</div>
<script type="text/javascript">
function show(self) {
var style=window.getComputedStyle?window.getComputedStyle(self,''):self.currentStyle;
alert(style.backgroundImage);
}
</script>
</body>
</html>