Please share the your code firstly .. I guess you want like this :
<head><title>Image Display Test
</title>
<script type="text/javascript">
function showImage(){
document.getElementById('loadingImage').style.visibility="visible";
}
</script>
</head>
<body>
<input type="button" value="Image Button" onclick="showImage();"/>
<img id="loadingImage" src="uorimagename.gif" style="visibility:hidden"/>
</body>
Thanks,
Ambesha