<div id="mydiv">foo</div>
<script>
document.getElementById("mydiv").onmouseover = function()
{
this.style.backgroundColor = "blue";
}
</script>// Creamos el evento mouseover para cada imagen
imagenes[i].addEventListener("mouseover", function(e){
document.getElementById("mostrar").style.backgroundImage="url('"+e.target.currentSrc+"')";
});
// Creamos el evento mouseout para cada imagen
imagenes[i].addEventListener("mouseout", function(e){
document.getElementById("mostrar").style.backgroundImage="";
});<img onmouseover="enlargeImage(this)" border="0" src="smiley.gif" alt="Smiley" width="32" height="32">
<script>
function enlargeImage(x) {
x.style.height = "64px";
x.style.width = "64px";
}
</script>