<html>
<head>
<script type="text/javascript">
function ini() {
document.getElementById('im').style.visibility = 'visible';
setTimeout('ocultar()',3000);
}
function ocultar() {
document.getElementById('im').style.visibility = 'hidden';
}
</script>
</head>
<body onload="setTimeout('ini()',3000)">
<img id="im" src="imagen1.jpg" style="visibility:hidden" />
</body>
</html>