验证码实现。。。。

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Drawing.Design;
using System.Drawing.Drawing2D;
using System.Drawing.Printing;
using System.Drawing.Imaging;
using System.IO;

public partial class CodeImage : System.Web.UI.Page
{
    private string CreateCheckCodeString()
    { //定义用于验证码的字符数组
        char[] AllCheckCodeArray ={ '0','1','2','3','4','5','6','7','8','9','A','B','C',
        'D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W',
        'X','Y','Z','a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q',
        'r','s','t','u','v','w','x','y','z'};
        //定义验证码字符串
        string randomcode = "";
        Random rd = new Random();
        //生成4位验证码字符串
        for (int i = 0; i < 4; i++)
            randomcode += AllCheckCodeArray[rd.Next(AllCheckCodeArray.Length)];
        return randomcode;
    }
    //生成验证码图片
    protected void Page_Load(object sender, EventArgs e)
    {
        //定义图片的宽度
        int ImageWidth = 55;
        //定义图片高度
        int ImageHeigh = 22;
        //定义字体，用于绘制文字
        Font font = new Font("Arial", 12, FontStyle.Bold);
        //定义画笔，用于绘制文字
        Brush brush = new SolidBrush(Color.Black);
        //定义钢笔，用于绘制干扰线
        Pen pen1 = new Pen(Color.FromArgb(255, 100, 100), 0);//这里也可以直接获得一个现有的color对象如：Color.Gold.我是为了美观所以定义和下面一样
        Pen pen2 = new Pen(Color.FromArgb(255, 100, 100), 0);//这里根据ARGB值定义获得了一个color对象
        //创建一个图像
        Bitmap BitImage = new Bitmap(ImageWidth, ImageHeigh);
        //从图像获取一个绘画面
        Graphics graphics = Graphics.FromImage(BitImage);
        //清除整个绘图画面并用颜色填充
        graphics.Clear(ColorTranslator.FromHtml("#F0F0F0"));//这里从HTML代码获取color对象
        //定义文字的绘制矩形区域
        RectangleF rect = new RectangleF(5, 2, ImageWidth, ImageHeigh);
        //定义一个随机数对象，用于绘制干扰线
        Random rand = new Random();
        //生成两条横向的干扰线
        for (int i = 0; i < 2; i++)
        {
            //定义起点
            Point p1 = new Point(0, rand.Next(ImageHeigh));
            //定义终点
            Point p2 = new Point(ImageWidth, rand.Next(ImageHeigh));
            //绘制直线
            graphics.DrawLine(pen1, p1, p2);
        }
        //生成两条纵向的干扰线
        for (int i = 0; i < 2; i++)
        {
            //定义起点
            Point p1 = new Point(rand.Next(ImageWidth), 0);
            //定义终点
            Point p2 = new Point(rand.Next(ImageWidth), ImageHeigh);
            //绘制直线
            graphics.DrawLine(pen2, p1, p2);
        }
        //绘制验证码文字
        string code=CreateCheckCodeString();
        Session["Code"] =code;  //保存验证码
        graphics.DrawString(code, font, brush, rect);
        //保存图片为gif格式
        BitImage.Save(Response.OutputStream, ImageFormat.Gif);
        //释放对象
        graphics.Dispose();
        BitImage.Dispose();
    }
}