如图所示：
随机产生指定位数的验证码的代码如下：
<script language="javascript">
function checkCode(digit){
//自动生成验证码
var result="";
for(i=0;i<parseInt(digit);i++){
result=result+(parseInt(Math.random()*10)).toString();
}
return result;
}
</script>
<script language="javascript">
function deal(){
result.innerHTML=" 产生的验证码："+checkCode(form1.digit.value);
}
</script>
<body>
<form name="form1" method="post" action="">
<table width="271" height="178" border="0" cellpadding="0" cellspacing="0" background="image/result.gif">
<tr>
<td valign="top"><table width="100%" height="150" border="0" cellpadding="0" cellspacing="0">
<tr>
<td width="15%" height="55"> </td>
<td width="69%" valign="bottom"><div ></td>
<td> </td>
</tr>
</table></td>
</tr>
</table>
</form>
</body>