實例如下：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>js驗證碼</title>
<style type="text/css">
.code
{
background-image:url(code.jpg);
font-family:Arial;
font-style:italic;
color:Red;
border:0;
padding:2px 3px;
letter-spacing:3px;
font-weight:bolder;
}
.unchanged
{
border:0;
}
</style>
<script language="javascript" type="text/javascript">
var code ; //在全局 定義驗證碼
function createCode()
{
code = "";
var codeLength = 4;//驗證碼的長度
var checkCode = document.getElementById("checkCode");
var selectChar = new Array(0,1,2,3,4,5,6,7,8,9,'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','wW','x','y','z');//所有候選組成驗證碼的字符，當然也可以用中文的
for(var i=0;i<codeLength;i++)
{
var charIndex = Math.floor(Math.random()*36);
code +=selectChar[charIndex];
}
// alert(code);
if(checkCode)
{
checkCode.className="code";
checkCode.value = code;
}
}
function validate ()
{
var inputCode = document.getElementById("input1").value;
if(inputCode.length <=0)
{
alert("請輸入驗證碼！");
}
else if(inputCode != code )
{
alert("驗證碼輸入錯誤！");
createCode();//刷新驗證碼
}
else
{
alert("OK");
}
}
</script>
</head>
<body onload="createCode()">
<form action="#">
<input type="text" id="input1" />
<input type="text" onclick="createCode()" readonly="readonly" id="checkCode" class="unchanged" style="width: 80px" /><br />
<input id="Button1" onclick="validate();" type="button" value="確定" />
</form>
</body>
</html>
