private void designerObject1_EditDesignerObject(object sender, EditDesignerObjectEventArgs e)
{
     DesignerObject desobj = (DesignerObject) sender;
     OpenFileDialog dialog = new OpenFileDialog();
     dialog.Filter = "JPEG files (*.jpg)|*.jpg|All files (*.*)|*.*";

     if(desobj.ObjectProperties.Contains("imagefile"))
          dialog.FileName = desobj.ObjectProperties["imagefile"].ToString();

     if(dialog.ShowDialog(e.DesignerWindow) == DialogResult.OK)
     {
          desobj.ObjectProperties["imagefile"] = dialog.FileName;
          e.HasChanged = true;
     }
}