var prm = Sys.WebForms.PageRequestManager.getInstance();

prm.add_initializeRequest(InitializeRequest);
prm.add_endRequest(EndRequest);
var postBackElement;
function InitializeRequest(sender, args) {
	if (prm.get_isInAsyncPostBack())
		args.set_cancel(true);
	postBackElement = args.get_postBackElement();
	if (img_id != null) {
		img_id.style.display = 'inline';
	}
}

function EndRequest(sender, args) {
	if (img_id != null) {
		img_id.style.display = 'none';
	}
	img_id = null;
}