Image preview function implemented by javascript

<script>
/*
Thumbnail image viewer-
?Dynamic Drive (www.dynamicdrive.com)
For full source code, usage terms, and 100&#39;s more DHTML scripts, visit http://dynamicdrive.com
*/
function enlarge(which,e){
//Render image code for IE 4+
if (document.all){
if (showimage.style.visibility=="hidden"){
showimage.style.left=document.body.scrollLeft+event.clientX
showimage.style.top=document.body.scrollTop+event.clientY
showimage.innerHTML=&#39;<img src="&#39;+which+&#39;">&#39;
showimage.style.visibility="visible"
}
else
showimage.style.visibility="hidden"
return false
}
//Render image code for NS 4
else if (document.layers){
if (document.showimage.visibility=="hide"){
document.showimage.document.write(&#39;<a href="#" rel="external nofollow" onMouseover="drag_dropns(showimage)"><img src="&#39;+which+&#39;" border=0></a>&#39;)
document.showimage.document.close()
document.showimage.left=e.x
document.showimage.top=e.y
document.showimage.visibility="show"
}
else
document.showimage.visibility="hide"
return false
}
//if NOT IE 4+ or NS 4, simply display image in full browser window
else
return true
}
</script>
<script language="JavaScript1.2">
//By Dynamicdrive.com
//drag drop function for NS 4////
/////////////////////////////////
var nsx
var nsy
var nstemp
function drag_dropns(name){
temp=eval(name)
temp.captureEvents(Event.MOUSEDOWN | Event.MOUSEUP)
temp.onmousedown=gons
temp.onmousemove=dragns
temp.onmouseup=stopns
}
function gons(e){
temp.captureEvents(Event.MOUSEMOVE)
nsx=e.x
nsy=e.y
}
function dragns(e){
temp.moveBy(e.x-nsx,e.y-nsy)
return false
}
function stopns(){
temp.releaseEvents(Event.MOUSEMOVE)
}
//drag drop function for IE 4+////
/////////////////////////////////
var dragapproved=false
function drag_dropie(){
if (dragapproved==true){
document.all.showimage.style.pixelLeft=tempx+event.clientX-iex
document.all.showimage.style.pixelTop=tempy+event.clientY-iey
return false
}
}
function initializedragie(){
if (event.srcElement.parentElement.id=="showimage"){
iex=event.clientX
iey=event.clientY
tempx=showimage.style.pixelLeft
tempy=showimage.style.pixelTop
dragapproved=true
document.onmousemove=drag_dropie
}
}
if (document.all){
document.onmousedown=initializedragie
document.onmouseup=new Function("dragapproved=false")
}
</script>

<p id="showimage" style="position:absolute;visibility:hidden"></p>

<a href="photo1.jpg" rel="external nofollow" onClick="return enlarge(&#39;photo1.jpg&#39;,event)">
<img src="thumbnail.gif" border="0">
</a>