C#.NET画验证码与Cookie验证

新建页面Code.aspx 在里面话验证码 后台代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            CreateCheckCodeImage(GenerateCheckCode());
        }
    }
    // 产生四位随机数的方法
    private string GenerateCheckCode()
    {
        int number;
        char code;
        //表示字符串为空，次字段为只读
        string checkCode = string.Empty;
        Random random = new Random();
        for (int i = 0; i < 4; i++)
        {
            number = random.Next();
            code = (char)('0' + (char)(number % 10));
            checkCode += code.ToString();
        }
        //将验证码保存到cookie中
        Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));
        return checkCode;
    }
    private void CreateCheckCodeImage(string checkCode)
    {
        //当随机数是空的时候或者 去掉空格还是空的时候
        if (checkCode == null || checkCode.Trim() == string.Empty)
            return;
        // 创建位图 4 * 12.5
        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);
            //画图片的毕竟噪音线
            for (int i = 0; i < 2; i++)
            {
                //产生随机的起始坐标和重点坐标
                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.Black), x1, y1, x2, y2);
            }
            //字体 大小12 加粗
            Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold));
            // 线性渐变封装
            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()));
            }
            // 花图片的边框线 矩形
            g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);
            //创建其支持存储区为内存的
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
            // 清楚缓冲区流中的所有内容输出
            Response.ClearContent();
            // 获取或设置输出流的格式
            Response.ContentType = "image/gif";
            //将一个二进制字符串 写入输出流   ms.ToArray()将整个流内容写入数组
            Response.BinaryWrite(ms.ToArray());

        }
        finally
        {
            // 释放资源
            g.Dispose();
            image.Dispose();
        }
    }
}

展示的页面：

验证码用HTML标签ima表示的 src的路径制定到Code.aspx
当点击图片的时候自动的刷新图片的路径 达到更换验证码的目的.。是通过js刷新img的src的路径实现的
<img id="Img1" alt="看不清，请点击我！" onclick="this.src=this.src+'?'" src="Code.aspx" style="width: 73px; height: 22px" align="left" />

验证页面的后台代码：

    protected void Button1_Click(object sender, EventArgs e)
    {
        string code = this.txtCode.Text;
        //从cookie中取出验证码
        HttpCookie cookie = Request.Cookies["CheckCode"];
        if (code == cookie.Value.ToString())
        {
            Response.Write("正确");
        }
        else
        {
            Response.Write("错误");
        }
    }

将验证码保存到cookie中：Response.Cookies.Add(new HttpCookie("CheckCode",checkCode));
从 cookie中取出验证码：HttpCookie cookie = Request.Cookies["CheckCode"];