轉自：http://espace.iteye.com/blog/202418
<pre name="code" class="html"><pre name="code" class="js"><!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>
<title>無標題頁</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 = 6;//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','W','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.toUpperCase() != code )/*此處修改過.toUpperCase()，全部改爲大寫驗證，.toLowerCase()全部改爲小寫驗證*/
{
alert("驗證碼輸入錯誤！");
createCode();//刷新驗證碼
}
else
{
alert("^-^ OK");
}
}
</script>
</head>
<body οnlοad="createCode()">
<form action="#">
<input type="text" id="input1" />
<input type="text" οnclick="createCode()" readonly="readonly" id="checkCode" class="unchanged" style="width: 80px" /><br />
<input id="Button1" οnclick="validate();" type="button" value="確定" />
</form>
</body>
</html></pre>
