.NET MVC 验证码

 // 随机生成指定长度的验证码字符串
        public ActionResult GetValidateCode(string key)
        {
            string codeStr = GetRandomCode();
            TempData[key] = codeStr;
            return File(GetVCode(codeStr), "image/gif");
        }

        private static Color BackColor = Color.White;
        private static int Width = 75;
        private static int Height = 30;
        private Random _random;

        private int _brushNameIndex;

        public byte[] GetVCode(string codeStr)
        {
            _random = new Random();
            using (Bitmap img = new Bitmap(Width, Height))
            {
                using (Graphics g = Graphics.FromImage(img))
                {
                    g.Clear(BackColor);//绘画背景颜色 
                    Paint_Text(g, codeStr);// 绘画文字 
                    Paint_TextStain(img);// 绘画噪音点
                    g.DrawRectangle(Pens.DarkGray, 0, 0, Width - 1, Height - 1);//绘画边框
                    using (System.IO.MemoryStream ms = new System.IO.MemoryStream())
                    {
                        //将图片 保存到内存流中
                        img.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
                        //将内存流 里的 数据  转成 byte 数组 返回
                        return ms.ToArray();
                    }
                }
            }
        }

        /// <summary>
        /// 绘画文字
        /// </summary>
        /// <param name="g"></param>
        private void Paint_Text(Graphics g, string code)
        {
            g.DrawString(code, GetFont(), GetBrush(), 5, 5);
        }

        /// <summary>
        /// 绘画文字噪音点
        /// </summary>
        /// <param name="g"></param>
        private void Paint_TextStain(Bitmap b)
        {
            string[] BrushName = new string[] {       "OliveDrab",
                                                  "ForestGreen",
                                                  "DarkCyan",
                                                  "LightSlateGray",
                                                  "RoyalBlue",
                                                  "SlateBlue",
                                                  "DarkViolet",
                                                  "MediumVioletRed",
                                                  "IndianRed",
                                                  "Firebrick",
                                                  "Chocolate",
                                                  "Peru", 
                                             };

            for (int n = 0; n < 480; n++)
            {
                b.SetPixel(_random.Next(Width), _random.Next(Height), Color.FromName(BrushName[_brushNameIndex]));
            }
        }

        /// <summary>
        /// 随机取一个字体
        /// </summary>
        /// <returns></returns>
        private Font GetFont()
        {
            string[] FontItems = new string[] { "Arial", "Helvetica", "Geneva", "sans-serif", "Verdana" };
            int fontIndex = _random.Next(0, FontItems.Length);
            FontStyle fontStyle = GetFontStyle(_random.Next(0, 2));
            return new Font(FontItems[fontIndex], 15, fontStyle);
        }

        /// <summary>
        /// 随机取一个笔刷
        /// </summary>
        /// <returns></returns>
        private Brush GetBrush()
        {
            Brush[] BrushItems = new Brush[]{   Brushes.OliveDrab,
                                            Brushes.ForestGreen,
                                            Brushes.DarkCyan,
                                            Brushes.LightSlateGray,
                                            Brushes.RoyalBlue,
                                            Brushes.SlateBlue,
                                            Brushes.DarkViolet,
                                            Brushes.MediumVioletRed,
                                            Brushes.IndianRed,
                                            Brushes.Firebrick,
                                            Brushes.Chocolate,
                                            Brushes.Peru, 
                                            };

            int brushIndex = _random.Next(0, BrushItems.Length);
            _brushNameIndex = brushIndex;
            return BrushItems[brushIndex];
        }

        /// <summary>
        /// 取一个字体的样式
        /// </summary>
        /// <param name="index"></param>
        /// <returns></returns>
        private FontStyle GetFontStyle(int index)
        {
            switch (index)
            {
                case 0:
                    return FontStyle.Bold;
                case 1:
                    return FontStyle.Italic;
                default:
                    return FontStyle.Regular;
            }
        }


        /// <summary>
        /// 取得一个 5 位的随机码
        /// </summary>
        /// <returns></returns>
        public string GetRandomCode(int len = 5)
        {
            return Guid.NewGuid().ToString().Substring(0, len);
        }