using System;using System.Drawing;using System.Drawing.Drawing2D;using System.Drawing.Imaging;using System.IO;namespace Common{    /// <summary>    /// 生成验证码的类    /// </summary>    public class ValidateCode    {        public ValidateCode()        {        }        /// <summary>        /// 验证码的最大长度        /// </summary>        public int MaxLength        {            get { return 10; }        }        /// <summary>        /// 验证码的最小长度        /// </summary>        public int MinLength        {            get { return 1; }        }        /// <summary>        /// 生成验证码        /// </summary>        /// <param name="length">指定验证码的长度</param>        /// <returns></returns>        public string CreateValidateCode(int length)        {            int[] randMembers = new int[length];            int[] validateNums = new int[length];            string validateNumberStr = "";            //生成起始序列值            int seekSeek = unchecked((int)DateTime.Now.Ticks);            Random seekRand = new Random(seekSeek);            int beginSeek = (int)seekRand.Next(0, Int32.MaxValue - length * 10000);            int[] seeks = new int[length];            for (int i = 0; i < length; i++)            {                beginSeek += 10000;                seeks[i] = beginSeek;            }            //生成随机数字            for (int i = 0; i < length; i++)            {                Random rand = new Random(seeks[i]);                int pownum = 1 * (int)Math.Pow(10, length);                randMembers[i] = rand.Next(pownum, Int32.MaxValue);            }            //抽取随机数字            for (int i = 0; i < length; i++)            {                string numStr = randMembers[i].ToString();                int numLength = numStr.Length;                Random rand = new Random();                int numPosition = rand.Next(0, numLength - 1);                validateNums[i] = Int32.Parse(numStr.Substring(numPosition, 1));            }            //生成验证码            for (int i = 0; i < length; i++)            {                validateNumberStr += validateNums[i].ToString();            }            return validateNumberStr;        }        /// <summary>        /// 创建验证码的图片        /// </summary>        /// <param name="containsPage">要输出到的page对象</param>        /// <param name="validateNum">验证码</param>        public byte[] CreateValidateGraphic(string validateCode)        {            Bitmap image = new Bitmap((int)Math.Ceiling(validateCode.Length * 12.0), 22);            Graphics g = Graphics.FromImage(image);            try            {                //生成随机生成器                Random random = new Random();                //清空图片背景色                g.Clear(Color.White);                //画图片的干扰线                for (int i = 0; i < 25; i++)                {                    int x1 = random.Next(image.Width);                    int x2 = random.Next(image.Width);                    int y1 = random.Next(image.Height);                    int y2 = random.Next(image.Height);                    g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);                }                Font font = new Font("Arial", 12, (FontStyle.Bold | FontStyle.Italic));                LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height),                 Color.Blue, Color.DarkRed, 1.2f, true);                g.DrawString(validateCode, font, brush, 3, 2);                //画图片的前景干扰点                for (int i = 0; i < 100; i++)                {                    int x = random.Next(image.Width);                    int y = random.Next(image.Height);                    image.SetPixel(x, y, Color.FromArgb(random.Next()));                }                //画图片的边框线                g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);                //保存图片数据                MemoryStream stream = new MemoryStream();                image.Save(stream, ImageFormat.Jpeg);                //输出图片流                return stream.ToArray();            }            finally            {                g.Dispose();                image.Dispose();            }        }        /// <summary>        /// 得到验证码图片的长度        /// </summary>        /// <param name="validateNumLength">验证码的长度</param>        /// <returns></returns>        public static int GetImageWidth(int validateNumLength)        {            return (int)(validateNumLength * 12.0);        }        /// <summary>        /// 得到验证码的高度        /// </summary>        /// <returns></returns>        public static double GetImageHeight()        {            return 22.5;        }    }}

        [AllowAnonymous]        public ActionResult GetValidateCode()        {            ValidateCode vCode = new ValidateCode();            string code = vCode.CreateValidateCode(4);            Session["ValidateCode"] = code;            byte[] bytes = vCode.CreateValidateGraphic(code);            return File(bytes, @"image/jpeg");        }

<img id="valiCode" style="cursor: pointer;" class="col-md-2 control-label" src="~/Account/GetValidateCode" alt="验证码" />

[HttpPost]        [AllowAnonymous]        [ValidateAntiForgeryToken]        public async Task<ActionResult> Login(LoginViewModel model, string returnUrl)        {            if (model.ValidCode != Session["ValidateCode"].ToString())            {                ModelState.AddModelError("", "验证码不正确.");                return View(model);            }            if (ModelState.IsValid)            {                var user = await UserManager.FindAsync(model.UserName, model.Password);                if (user != null)                {                    await SignInAsync(user, model.RememberMe);                    return RedirectToLocal(returnUrl);                }                else                {                    ModelState.AddModelError("", "Invalid username or password.");                }            }            // 如果我们进行到这一步时某个地方出错，则重新显示表单            return View(model);        }

@section Scripts {    @Scripts.Render("~/bundles/jqueryval")<script type="text/javascript">    $(function () {        $("#valiCode").bind("click", function () {            this.src = http://www.mamicode.com/"../Account/GetValidateCode?time=" + (new Date()).getTime();        });    });</script>}