MVC生成图片验证码，可指定位数

前台：

<h2>mvc后台生成验证码,可指定位数</h2>
<img id="gc"  src="GetValidateCode"  onclick="this.src='GetValidateCode?r=' + Math.random()" />
<button onclick="javascript:document.getElementById('gc').src='GetValidateCode?r=' + Math.random()">刷新</button>

后台：

public ActionResult yzm() 
      {
          return View();
      }
      /// <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();
          }
      }
 
      public ActionResult GetValidateCode()
      {
 
          int code = new Random().Next(1000, 10000);
          Session["ValidateCode"] = code;
          byte[] bytes = CreateValidateGraphic(code.ToString());
          return File(bytes, @"image/jpeg");
      }