验证码

1.把这个生成验证码的类加入项目中;
/****************************************************************/
using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Drawing.Drawing2D;
using System.Web;
using System.Web.UI;
using System.Web.SessionState;
/// <summary>
///图片验证码
/// </summary>
public class Validatenumimage
{
    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();
        }
        //将生成的验证码加入Session中
        HttpContext.Current.Session.Add("CheckCode", checkCodeToLower());
        // 使用Cookies取验证码的值
        //Response.Cookies.Add(new HttpCookie("CheckCode", checkCode.ToLower()));
        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);
            HttpContext.Current.Response.ClearContent();
            HttpContext.Current.Response.C;
            HttpContext.Current.Response.BinaryWrite(ms.ToArray());
        }
        finally
        {
            g.Dispose();
            image.Dispose();
        }
    }
    public void CreateCheckCodeImage()
    {
        CreateCheckCodeImage(GenerateCheckCode());
    }
}
/****************************************************************/
2.再新建一个空ASPX页面MarkCheckCode.aspx;
3.在该页面的Page_Load事件里面调用该Validatenumimage类的方法：
/****************************************************************/
Validatenumimage markCheckCode = new Validatenumimage();
  markCheckCode.CreateCheckCodeImage();
/****************************************************************/
4.在要使用验证码的页面里加入该标记; 
/****************************************************************/
<img src="MarkCheckCode.aspx" alt="若看不清,点击更换一张!!"　ｏｎｃｌｉｃｋ＝“ｔｈｉｓ。ｓｒｃ＝ｔｈｉｓ。ｓｒｃ＋‘？’” />
论坛机制的影响：  ｏｎｃｌｉｃｋ在标记中无法正常显示，大家注意修改一下
/****************************************************************/