function check_loginform () {
	var login_id = document.getElementById("login_id").value;
	var login_pass = document.getElementById("login_pass").value;
	var login_valid = document.getElementById("login_valid").value;
	if (login_id ==""){
		alert("请输入登录帐号");
		return false;
	}
	if (login_pass ==""){
		alert("请输入登录密码");
		return false;
	}
	if (login_valid == "") {
		alert("请输入如图所示的验证码");
		return false;
	}
	return true;
}