hola prueba esto
esta hecho con un texto pero en ves del texto modificalo por una imagen
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Untitled Document</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<script language="JavaScript" type="text/JavaScript">
<!--
function MM_reloadPage(init) { //reloads the window if Nav4 resized
if (init==true) with (navigator) {if ((appName=="Netscape")&&(parseInt(appVersion)==4)) {
document.MM_pgW=innerWidth; document.MM_pgH=innerHeight; onresize=MM_reloadPage; }}
else if (innerWidth!=document.MM_pgW || innerHeight!=document.MM_pgH) location.reload();
}
MM_reloadPage(true);
function MM_findObj(n, d) { //v4.01
var p,i,x; if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
for(i=0;!x&&d.layers&&i<d.layers.length;i++) x=MM_findObj(n,d.layers[i].document);
if(!x && d.getElementById) x=d.getElementById(n); return x;
}
function MM_setTextOfLayer(objName,x,newText) { //v4.01
if ((obj=MM_findObj(objName))!=null) with (obj)
if (document.layers) {document.write(unescape(newText)); document.close();}
else innerHTML = unescape(newText);
}
//-->
</script>
</head>
<body>
<div id="Layer1" style="position:absolute; left:117px; top:72px; width:146px; height:122px; z-index:1"></div>
<a href="javascript
:;" onMouseOver="MM_setTextOfLayer('Layer1','','hola como estamos')" onMouseOut="MM_setTextOfLayer('Layer1','','')">hol a</a>
</body>
</html>
espero que te sirva
saludos