check following code
<SCRIPT type="text/javascript">
<!--
function checkImg(objImg)
{
document.getElementById("previewImg").src=objImg.value;
}
</SCRIPT>
</HEAD>
<BODY>
<INPUT type="file" id="picField" onchange="checkImg(this)">
<IMG id="previewImg" alt="Preview">
</BODY>
you can check
this[
^] link also.-->