This is the code that shows how to preview the image on a dialog.
<div id="dlg" class="easyui-dialog" title="Basic Dialog" style="width:400px;height:200px;padding:10px">
<input class="easyui-filebox" data-options="
width: '100%',
accept: 'image/*',
onChange: function(){
var files = $(this).filebox('files');
var url = window.URL.createObjectURL(files[0]);
$('#img').attr('src',url)
}
">
<img id="img">
</div>