asp.net下登陆验证码实现

登陆页面-验证码的实现：

view页面：

<asp:Content ID="loginContent" ContentPlaceHolderID="MainContent" runat="server">
    <h2>Log On</h2>
    <p>
        Please enter your username and password. <%= Html.ActionLink("Register", "Register") %> if you don't have an account.
    </p>

    <% using (Html.BeginForm()) { %>
        <%= Html.ValidationSummary(true, "Login was unsuccessful. Please correct the errors and try again.") %>
        <div>
            <fieldset>
                <legend>Account Information</legend>
               
                <div class="editor-label">
                    <%= Html.LabelFor(m => m.UserName) %>
                </div>
                <div class="editor-field">
                    <%= Html.TextBoxFor(m => m.UserName) %>
                    <%= Html.ValidationMessageFor(m => m.UserName) %>
                </div>
               
                <div class="editor-label">
                    <%= Html.LabelFor(m => m.Password) %>
                </div>
                <div class="editor-field">
                    <%= Html.PasswordFor(m => m.Password) %>
                    <%= Html.ValidationMessageFor(m => m.Password) %>
                </div>
               
                <div class="editor-label">
                    <%= Html.CheckBoxFor(m => m.RememberMe) %>
                    <%= Html.LabelFor(m => m.RememberMe) %>
                </div>
                <div>
                <table>
                <tr>
                <td>验证码</td>
                <td><img src="CheckImage.aspx" width="120" height="30" style="cursor:hand"
                     onclick="this.src='CheckImage.aspx?id='+Math.random()*10000" alt="点击刷新验证码" /></td>
                </tr>
                </table>
                </div>
                <p>
                    <input type="submit" value="Log On" />
                </p>
            </fieldset>
        </div>
    <% } %>

后台：

protected void Page_load(object sender,EventArgs e)

{

//验证码中可能出现的字符集合

string checkCodeString = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
            int length = checkCodeString.Length;

            Font font = new Font("宋体",24,FontStyle.Bold);//设置宋体绘制验证字符，并加粗
            Brush brush = null;//绘制验证码的brush对象
            Color brushColor = new Color();//绘制验证码的颜色

            string checkCode = string.Empty;//显示给用户的验证码字符串
            string code = string.Empty;//要绘制的验证码字符

            Bitmap image = new Bitmap(80,40);
            Graphics g = Graphics.FromImage(image);//实例化图表
            g.Clear(Color.White);

            Random random = new Random();//生成随机数
            for (int i = 0; i < 4; i++)
            {
                int current = random.Next(DateTime.Now.Millisecond) % length;//采用模运算，保证current不会超过验证码集合的长度
                code = checkCodeString.Substring(current,1);//从验证码中随机截取一个字符来绘制
                checkCode = checkCode + code;
                brushColor = Color.FromArgb(random.Next(255),random.Next(255),random.Next(255));//随机生成绘制验证码字符的颜色
                brush = new SolidBrush(brushColor);
                g.DrawString(code,font,brush,i*15+2,2);//绘制刚刚得到的字符串，(i*15+2)用来设定X轴，以区分字符间距
            }
            Response.Clear();//清除无用信息
            Response.ContentType = "image/pjpeg";
            image.Save(Response.OutputStream,ImageFormat.Jpeg);//将图像保存到response输出流

            Session["CheckCode"] = checkCode;//保存，以便于同用户输入对比
            image.Dispose();//释放资源
            Response.End();//结束输出

}