怎么验证输入的验证码是否正确

<ubb>
<script type="text/javascript">
var SP = "http://image.club.sohu.com/js/";
document.write("<scr"+"ipt type='text/javascript' src='"+ SP + "club_global.js'></scr"+"ipt>");
var SL = ["http://image.club.sohu.com/js/prototype_1.5.0.js", "http://image.club.sohu.com/js/validator_1.0.2.js", "http://image.club.sohu.com/js/club_msgnick_1.0.1.js"];
</script>
<script type="text/javascript">
lsl(SL);
</script>
<script type="text/javascript">
//刷新验证码图片
var refreshvc = function()
{
//生成0-9随机数
var x = new Date();
var dt = x.getTime();
var refresh = dt%9; 
//更新图片
$("vcodeimage").src="http://service.club.sohu.com/vcode/vcode.php?vcode=8d2zM23d24K1f27zA8e23xB.f29TM2c9f0E4ec2TK145cxT.e95jP1a6a%2CE6470VL1326YH.13dVU9c4eXB9a96UB+a83UT+25dBQ+474JQ+917HE+4ddOY+c17NV+2b4J%2C+614JQ+1c5OM+02cJM+aa9NM+495Gk+9f3CO+84bQE+7e0SN+0a2Rc+996EM+&refresh="+refresh;
};
</script>
<form>
<!--vcode by jimmy 20060120-->
<ul>
<li nowrap>输入验证码:</li>
<li>
<input type=text name=code id="code" Datatype='Require' msg='请填写验证码' okmsg="√" value='' size=6 class="input_gr"><input type=hidden name=vcode id="vcode" value='8d2zM23d24K1f27zA8e23xB.f29TM2c9f0E4ec2TK145cxT.e95jP1a6a,E6470VL1326YH.13dVU9c4eXB9a96UB a83UT 25dBQ 474JQ 917HE 4ddOY c17NV 2b4J, 614JQ 1c5OM 02cJM aa9NM 495Gk 9f3CO 84bQE 7e0SN 0a2Rc 996EM '></li>
 <li><img id="vcodeimage" name="vcodeimage" src=http://service.club.sohu.com/vcode/vcode.php?vcode=8d2zM23d24K1f27zA8e23xB.f29TM2c9f0E4ec2TK145cxT.e95jP1a6a%2CE6470VL1326YH.13dVU9c4eXB9a96UB+a83UT+25dBQ+474JQ+917HE+4ddOY+c17NV+2b4J%2C+614JQ+1c5OM+02cJM+aa9NM+495Gk+9f3CO+84bQE+7e0SN+0a2Rc+996EM+>
<a onmouseover="this.style.cursor='pointer'" onclick="refreshvc()"style="color:red;">看不清数字？请在刷新一遍</a></li>
</ul>
 <!--vcode end-->
</form>
</ubb>