C# 验证码生成（MVC和非MVC两种方式）

        /// <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 rand;
            char code;
            string randomcode = String.Empty;
            //生成一定长度的验证码  
            System.Random random = new Random();
            for (int i = 0; i < length; i++)
            {
                rand = random.Next();
                if (rand % 3 == 0)
                {
                    code = (char)('A' + (char)(rand % 26));
                }
                else
                {
                    code = (char)('0' + (char)(rand % 10));
                }
                randomcode += code.ToString();
            }
            return randomcode;
        }

        /// <summary>
        /// 创建验证码的图片(非MVC模式下使用)
        /// </summary>
        /// <param name="containsPage">要输出到的page对象</param>
        /// <param name="validateCode">验证码</param>
        /// <param name="fontSize">字体大小</param>
        public void CreateValidateGraphic(HttpContext containsPage, string validateCode, int fontSize = 20)
        {
            Bitmap image = new Bitmap((int)Math.Ceiling(validateCode.Length * 21.0), (int)Math.Ceiling(fontSize * 1.8));
            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", fontSize, (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
                containsPage.Response.Clear();
                containsPage.Response.ContentType = "image/jpeg";
                containsPage.Response.BinaryWrite(stream.ToArray());
            }
            finally
            {
                g.Dispose();
                image.Dispose();
            }
        }

        /// <summary>
        /// 创建验证码的图片(MVC模式下使用)
        /// </summary>
        /// <param name="validateCode">验证码</param>
        /// <param name="fontSize">字体大小</param>
        public byte[] CreateValidateGraphic(string validateCode, int fontSize = 20)
        {
            Bitmap image = new Bitmap((int)Math.Ceiling(validateCode.Length * 21.0), (int)Math.Ceiling(fontSize * 1.8));
            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", fontSize, (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>
        /// 验证码Key
        /// </summary>
        public const string ValidateCodeKey = "ValidateCode";

      /// <summary>
        /// 获取验证码
        /// </summary>
        /// <returns></returns>
        [OutputCache(Duration = 0)]
        public ActionResult VerifyCode()
        {
            ValidateCode vCode = new ValidateCode();
            string code = vCode.CreateValidateCode(5);
            Session[ConstHelper.ValidateCodeKey] = code;
            byte[] bytes = vCode.CreateValidateGraphic(code);
            return File(bytes, @"image/jpeg");
        }