ASP.NET MVC 登录验证码

图片验证码HTML页面：

LoginController.cs

        //生成验证码
        [HttpGet]
        public ActionResult VerifyCode()
        {
            return File(new VerifyCode().GetVerifyCode(0,0,0), @"image/Gif");
        }

VerifyCode.cs

public byte[] GetVerifyCode(int width, int height, int length)
        {
            int codeW = width;
            int codeH = height;
            int codeL = length;
            //设置默认最小值
            if (codeW < 80)
            {
                codeW = 80;
            }
            if (codeH < 30)
            {
                codeH = 30;
            }
            if(codeL < 4)
            {
                codeL = 4;
            }
            string chkCode = string.Empty;
            //噪点的颜色列表
            Color[] color = {Color.Black,Color.Red,Color.Blue,Color.Green, Color.Orange, Color.Brown, Color.Brown, Color.DarkBlue };

            //字体列表
            string[] font = { "Times New Roman" };

            char[] character = { '2', '3', '4', '5', '6', '8', '9', 'a', 'b', 'd', 'e', 'f', 'h', 'k', 'm', 'n', 'r', 'x', 'y', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'R', 'S', 'T', 'W', 'X', 'Y' };
            Random random = new Random();
            //生成随机的验证码
            for (int i = 0; i < codeL; i++)
            {
                chkCode += character[random.Next(character.Length)];
            }
            WebHelper.WriteSession("session_verifycode", Md5Helper.MD5(chkCode.ToLower(),16));
             
             
            //创建画布
            Bitmap bmp = new Bitmap(codeW, codeH);
            Graphics g = Graphics.FromImage(bmp);
            g.Clear(Color.White);
            //画噪线 
            for (int i = 0; i < 1; i++)
            {
                int x1 = random.Next(codeW);
                int y1 = random.Next(codeH);
                int x2 = random.Next(codeW);
                int y2 = random.Next(codeH);
                Color clr = color[random.Next(color.Length)];
                g.DrawLine(new Pen(clr), x1, y1, x2, y2);
            }
            //画验证码字符串 
            for (int i = 0; i < chkCode.Length; i++)
            {
                string fnt = font[random.Next(font.Length)];
                Font ft = new Font(fnt, 16);
                Color clr = color[random.Next(color.Length)];
                g.DrawString(chkCode[i].ToString(), ft, new SolidBrush(clr), (float)i * 18, (float)0);
            }
            //将验证码图片写入内存流，并将其以 "image/Png" 格式输出 
            MemoryStream ms = new MemoryStream();
            try
            {
                bmp.Save(ms, ImageFormat.Png);
                return ms.ToArray();
            }
            catch (Exception)
            {
                return null;
            }
            finally
            {
                g.Dispose();
                bmp.Dispose();
            }
        }

点击图片切换验证码

           //点击切换验证码
            $("#login_verifycode").click(function () {
                $("#verifycode").val('');
                $("#login_verifycode").attr("src", contentPath + "/Login/VerifyCode?time=" + Math.random());
            });