Jeg fandt ud af løsningen ;o)
<script>
function mouser(){
if(event.x < originalimg.width && event.y < originalimg.height){
if(originalimg.height > parseInt(event.y)+(parseInt(sel.style.height.replace('px','')))/2 && event.y-(parseInt(sel.style.height.replace('px',''))/2) >= 0){
sel.style.top=event.y-(parseInt(sel.style.height.replace('px',''))/2);
}
if(originalimg.width > parseInt(event.x)+(parseInt(sel.style.width.replace('px','')))/2 && event.x-(parseInt(sel.style.width.replace('px',''))/2) >= 0){
sel.style.left=event.x-(parseInt(sel.style.width.replace('px',''))/2);
}
}
}
function capture(){
location.href ='?id=crop&x='+sel.style.left.replace('px','')+'&y='+sel.style.top.replace('px','')+'&w='+sel.style.width.replace('px','')+'&h='+sel.style.height.replace('px','');
}
</script>
</head>
<body leftmargin="0" rightmargin="0" topmargin="0" bottommargin="0" onmousemove="mouser()" onscroll="mouser()">
<div id="sel" onmousedown="capture()" style="left:0; top:0; border-width:1; border-style:solid; border-color:black; width:50; height:50; position:absolute; background-color:white; filter:progid:DXImageTransform.Microsoft.Alpha( Opacity=33, FinishOpacity=33, Style=1, StartX=0, FinishX=100, StartY=0, FinishY=100)"></div>
<div id="container" onkeydown="return false" style="overflow:visible; width:0; height:0"><img imagetoolbar="no" id="originalimg" src="<%=pic%>"></div>
