using System;
using System.Collections.Generic;
using System.Web;
using System.Web.Mvc;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing;
namespace Angel.Web.Controllers
{
  public class CheckCodeController : Controller
  {
    //
    // GET: /CheckCode/
    public ActionResult Index()
    {
      this.CreateCheckCodeImage(GenerateCheckCode());
      return View();
    }
    private string GenerateCheckCode()
    {
      int number;
      char code;
      string checkCode = String.Empty;
      System.Random random = new Random();
      for (int i = 0; i < 5; i++)
      {
        number = random.Next();
        if (number % 2 == 0)
          code = (char)('0' + (char)(number % 10));
        else
          code = (char)('A' + (char)(number % 26));
        if (code == '0' || code == 'o' || code == 'L' || code == 'I')
        {
          i = i - 1;
        }
        else
        {
          checkCode += code.ToString();
        }
      }
      // Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));
      Session.Contents["checkcode"] = checkCode;
      return checkCode;
    }
    private void CreateCheckCodeImage(string checkCode)
    {
      if (checkCode == null || checkCode.Trim() == String.Empty)
        return;
      System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 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);
        //画图片的背景噪音线
        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 System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
        System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
        g.DrawString(checkCode, font, brush, 2, 2);
        //画图片的前景噪音点
        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);
        System.IO.MemoryStream ms = new System.IO.MemoryStream();
        image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
        Response.ClearContent();
        Response.ContentType = "image/Gif";
        Response.BinaryWrite(ms.ToArray());
      }
      finally
      {
        g.Dispose();
        image.Dispose();
      }
    }
  }
}

/// <summary>
/// MVC为了获取session参数
/// </summary>
public override void Init()
{
  PostAuthenticateRequest += (s, e) => HttpContext.Current.SetSessionStateBehavior(SessionStateBehavior.Required);
  base.Init();
}
void MvcApplication_PostAuthenticateRequest(object sender, EventArgs e)
{
  HttpContext.Current.SetSessionStateBehavior(SessionStateBehavior.Required);
}

<img name="img1" id="img1" style="position:absolute;top:5px;right:36px!important;z-index:1000;" alt="单击图片刷新验证码" src="CheckCode/Index" <br>onclick="JavaSccript:reloadImage('CheckCode/Index');" /><br><script type="text/javascript">
function reloadImage(url) {
document.getElementById("img1").src = url + '?abc=' + Math.random();
}
  </script>