public class CodeController : Controller

    {

        private const string CODE = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";//验证码字符池

        private const int COUNT = ;//验证码字符个数

        private const int WIDTH = ;//图片宽

        private const int HEIGHT = ;//图片高

        // 产生验证码

        private string GetCode()

        {

            Random r = new Random();

            int length = CODE.Length;

            StringBuilder sCode = new StringBuilder();

            for (int i = ; i < COUNT; i++)

            {

                int index = r.Next(, length);

                sCode.Append(CODE[index]);

            }

            return sCode.ToString();

        }

        /// <summary>

        /// 创建验证码图片

        /// </summary>

        /// <returns>图片文件</returns>

        public ActionResult Code()

        {

            //画背景图

            Bitmap bmp = new Bitmap(WIDTH, HEIGHT);//创建位图(宽，高)

            Graphics g = Graphics.FromImage(bmp);//创建画布

            g.FillRectangle(Brushes.LightGray, , , WIDTH, HEIGHT);//为画布填充底色(颜色，起始位置，终止位置)

            //画验证码

            string code = this.GetCode();//取出验证码

            this.Session.Add("code", code);//将当前验证码存入Session

            Font f = new Font("微软雅黑", , FontStyle.Italic);//自定义文本格式(字体，字号，字形)

            g.DrawString(code, f, Brushes.Black, , );//在画布上写入文本(内容，格式，颜色，起始位置)

            //画干扰点或线

            Random r = new Random();

            for (int i = ; i < ; i++)

            {

                Color color = Color.FromArgb(r.Next(, ), r.Next(, ), r.Next(, ));//随机颜色

                Pen pen = new Pen(color);//创建线笔(颜色)

                int x = r.Next(, WIDTH);

                int y = r.Next(, HEIGHT);

                int xDir = r.Next();

                int yDir = r.Next();

                g.DrawLine(pen, x, y, x + xDir, y + yDir);//在画布上画短线(线笔，起始位置，终止位置)

            }

            ReturnResult result = new ReturnResult() { Result=true};

            //向客户端输出

            using (MemoryStream mStream = new MemoryStream())//创建内存流对象

            {

                bmp.Save(mStream, ImageFormat.Jpeg);//保存位图至内存流(内存流，格式)

                byte[] data = mStream.ToArray();//将内存流转换成字节数组

                return this.File(data, "application/image");//向客户端输出文件(输出内容，内容类型)

            }

        }

    }

           <div class="Mask_div1 clearfix">

                <p class="Mask_p1 fl">验证码：</p>

                <input type="text" class="Mask_text1 fl" id="codetxt" />

                <img src="/code/code" id="code" class="Mask_ing fl" />

                <a href="javascript:void(0)" id="change" class="Mask_a1 fl">【刷新】</a>

            </div>

<script>
$(function(){
$("#change").click(function () {
                var url = "/code/code?t=" + Date();
                $("#code").attr("src", url);
            });

})
 </script>