function SwitchImg()
{
var rem, keep=0, store, obj, switcher=new Array, history=document.Data;
for (rem=0; rem < (SwitchImg.arguments.length-2); rem+=3) {
store = SwitchImg.arguments[(navigator.appName == 'Netscape')?rem:rem+1];
if ((store.indexOf('document.layers[')==0 && document.layers==null) ||
(store.indexOf('document.all[')==0 && document.all==null))
store = 'document'+store.substring(store.lastIndexOf('.'),store.length);
obj = eval(store);
if (obj != null) {
switcher[keep++] = obj;
switcher[keep++] = (history==null || history[keep-1]!=obj)?obj.src:history[keep];
obj.src = SwitchImg.arguments[rem+2];
} }
document.Data = switcher;
}
function RestoreImg()
{
if (document.Data != null)
for (var rem=0; rem<(document.Data.length-1); rem+=2)
document.Data[rem].src=document.Data[rem+1];
}
<a href=" " onMouseOut="RestoreImg()" onMouseOver="SwitchImg( ' ',' ',' ')"><img src=" "></a><BR>