[Código Javascript] Borde al pasar mouse en una imagen

<style type="text/css">
.borderimage{
border:1px solid white;
}
</style> <script language="JavaScript1.2">

/*
Highlight Image Script II-
© Dynamic Drive (www.dynamicdrive.com)
For full source code, usage terms, and 100's more DHTML scripts, visit http://dynamicdrive.com
*/

function borderit(which,color){
//if IE 4+ or NS 6+
if (document.all||document.getElementById){
which.style.borderColor=color
}
}

</script>