JavaScript 验证码的实例代码(附效果图)

效果如下：

代码如下:

<html xmlns="http://www.w3.org/1999/xhtml">

<head runat="server">
    <title></title>
    <style type="text/css">
    .code
    {
            background:url(code_bg.jpg);
            font-family:Arial;
            font-style:italic;
             color:blue;
             font-size:30px;
             border:0;
             padding:2px 3px;
             letter-spacing:3px;
             font-weight:bolder;            
             float:left;           
             cursor:pointer;
             width:150px;
             height:60px;
             line-height:60px;
             text-align:center;
             vertical-align:middle;

}
    a
    {
        text-decoration:none;
        font-size:12px;
        color:#288bc4;
        }
    a:hover
    {
       text-decoration:underline;
        }
    </style>
    <script language="javascript" type="text/javascript">

var code;
        function createCode() {
            code = "";
            var codeLength = 6; //验证码的长度
            var checkCode = document.getElementById("checkCode");
            var codeChars = 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',
            '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'); //所有候选组成验证码的字符，当然也可以用中文的
            for (var i = 0; i < codeLength; i++)
            {
                var charNum = Math.floor(Math.random() * 52);
                code += codeChars[charNum];
            }
            if (checkCode)
            {
                checkCode.className = "code";
                checkCode.innerHTML = code;
            }
        }
        function validateCode()
        {
            var inputCode = document.getElementById("inputCode").value;
            if (inputCode.length <= 0)
            {
                alert("请输入验证码！");
            }
            else if (inputCode.toUpperCase() != code.toUpperCase())
            {
                alert("验证码输入有误！");
                createCode();
            }
            else
            {
                alert("验证码正确！");
            }       
        }   
     </script>

</head>
<body onload="createCode()">
    <form id="form1" runat="server" onsubmit="validateCode()">
    <div>
    <table border="0" cellspacing="5" cellpadding="5" >
        <tr>
            <td></td><td> <div class="code" id="checkCode" onclick="createCode()" ></div></td>
            <td><a  href="#" onclick="createCode()">看不清换一张</a></td>
        </tr>
        <tr>
            <td>验证码：</td><td><input  style="float:left;" type="text"   id="inputCode" /></td><td>请输入验证码</td>
        </tr>
        <tr><td></td><td><input id="Button1"  onclick="validateCode();" type="button" value="确定" /></td><td></td>
        </tr>
    </table>
    </div>
    </form>
</body>
</html>