随机生成登录验证码（4位）

前：

<script src="~/Scripts/jquery-1.10.2.min.js"></script>

<input type="text" name="code" id="code" lay-verify="required|num" autocomplete="off" placeholder="输入验证码">
<img src="../Home/YZM" onclick="chageimg()" height="28" id="refImg" style="cursor:pointer;" title="点击刷新" />
<input type="button" value="登录" onclick="Login()"/>



<script>
    function chageimg() {      
        $("#refImg").attr("src", "../Home/YZM?timestamp=" + new Date().getTime());
    }

    function Login() {
        var code = $("#code").val();
        $.ajax({
            type: 'Post',
            url: '/Home/YZMCheck',
            data: { code: code },
            success: function (data) {
                if (data.succ) {
                    alert(data.msg);
                }
                else {
                    alert(data.msg);
                    return false;
                }
            },
            complete: function (data) {

            }
        })


    }
</script>

后：

public ActionResult Index()
        {
            return View();
            
        }

        /// <summary>
        /// 生成验证码
        /// </summary>
        /// <returns></returns>
        public ActionResult YZM()
        {
            string oldcode = TempData["SecurityCode"] as string;
            string code = CreateRandomCode(4); //验证码的字符为4个
            Session["YZMCode"] = code;
            TempData["SecurityCode"] = code; //验证码存放在TempData中
            return File(CreateValidateGraphic(code), "image/Jpeg");
        }

        /// <summary>
        /// 验证码校验
        /// </summary>
        /// <param name="code"></param>
        /// <returns></returns>
        public JsonResult YZMCheck(string code)
        {
            string msg = null;//返回的信息
            bool succ = false;//是否成功
            string yzmcode = Session["YZMCode"].ToString();
            if(code==yzmcode)
            {
                succ = true;
                msg = "验证成功！";
            }
            else
            {
                succ = false;
                msg = "验证失败！";
            }

            var json = new { msg = msg, succ = succ };
            return Json(json);
        }


        /// <summary>
        /// 生成随机的字符串
        /// </summary>
        /// <param name="codeCount"></param>
        /// <returns></returns>
        public string CreateRandomCode(int codeCount)
        {
            string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,a,b,c,d,e,f,g,h,i,g,k,l,m,n,o,p,q,r,F,G,H,I,G,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,s,t,u,v,w,x,y,z";
            string[] allCharArray = allChar.Split(',');
            string randomCode = "";
            int temp = -1;
            Random rand = new Random();
            for (int i = 0; i < codeCount; i++)
            {
                if (temp != -1)
                {
                    rand = new Random(i * temp * ((int)DateTime.Now.Ticks));
                }
                int t = rand.Next(35);
                if (temp == t)
                {
                    return CreateRandomCode(codeCount);
                }
                temp = t;
                randomCode += allCharArray[t];
            }
            return randomCode;
        }

        /// <summary>
        /// 创建验证码图片
        /// </summary>
        /// <param name="validateCode"></param>
        /// <returns></returns>
        public byte[] CreateValidateGraphic(string validateCode)
        {
            Bitmap image = new Bitmap((int)Math.Ceiling(validateCode.Length * 16.0), 27);
            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, x2, y1, y2);
                }
                Font font = new Font("Arial", 13, (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);

                //画图片的前景干扰线
                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();
            }
        }