自己在專案中經常使用的驗證碼，樣式還不錯，簡單又好用，為了以後方便，寫入部落格以便以後使用檢視

寫一個一般處理程式checkcode.ashx，返回生成的驗證碼

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Web;
using System.Web.SessionState;

namespace VIPSite
{
    /// <summary>
    /// checkcode 的摘要說明
    /// </summary>
    public class checkcode : IHttpHandler,IRequiresSessionState
    {
        HttpContext context;
        public void ProcessRequest(HttpContext context1)
        {
           
            this.context = context1;
            CreateCheckCodeImage(GenerateCheckCode());
        }

        public bool IsReusable
        {
            get
            {
                return false;
            }
        }

        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));

                checkCode += code.ToString();
            }
            context.Session["chkcode"] = checkCode;
            return checkCode;
        }

        private void CreateCheckCodeImage(string checkCode)
        {
            if (checkCode == null || checkCode.Trim() == String.Empty)
                return;
            Bitmap image = new Bitmap((int)Math.Ceiling((checkCode.Length * 20.5)), 32);
            Graphics g = Graphics.FromImage(image);

            try
            {
                //生成隨機生成器
                Random random = new Random();

                //清空圖片背景色
                g.Clear(Color.White);

                //畫圖片的背景噪音線
                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", 20, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
                System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(3, 3, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
                g.DrawString(checkCode, font, brush, 2, 2);

                //畫圖片的前景噪音點
                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()));
                }

                //畫圖片的邊框線
                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);
                context.Response.ClearContent();
                context.Response.ContentType = "image/Gif";
               context.Response.BinaryWrite(ms.ToArray());
            }
            finally
            {
                g.Dispose();
                image.Dispose();
            }
        }
    }
}
 

<script type="text/javascript">
        function changeCode() {
            document.getElementById("imgCode").src = "/ashx/checkcode.ashx?d=" + new Date().getMilliseconds();
        }
    </script>
<img src="/ashx/checkcode.ashx" id="imgCode" onclick="return changeCode()" />

if (Session["chkcode"] == null)
                {
                    string script = "alert('驗證碼已過期，請重新重新整理頁面!');location='" + ConfigHelper.Domain + "/lg";
                    PageHelper.RegScript(Page, script);
                    return;
                }


                if (txtcode.Text.Trim().ToLower() != Session["chkcode"].ToString().ToLower())
                {
                    string script = "alert('驗證碼不正確，請重新輸入!');";
                    PageHelper.RegScript(Page, script);
                }
                else
                {
                    Session.Remove("chkcode");
                }
 

至此一個完整的驗證碼的功能就完成了