生成验证码图片

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.Imaging;
using System.Drawing.Drawing2D;

namespace WebApplication4
{
    public partial class login : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            Response.Clear();
            Random r = new Random((int)DateTime.Now.Ticks);
            int number = r.Next(1000, 9999);
            Session["validateCode"] = number;

            Bitmap bmp = new Bitmap(50, 25);
            Graphics g = Graphics.FromImage(bmp);
            HatchBrush hb = new HatchBrush(HatchStyle.Cross, Color.Green, Color.White);

            g.FillRectangle(hb, 0, 0, 25, 50);
            g.DrawString(number.ToString(), new Font("arial", 14), new SolidBrush(Color.Red), 0, 0);
            bmp.Save(Response.OutputStream, ImageFormat.Jpeg);
            hb.Dispose();
            g.Dispose();
            bmp.Dispose();
            Response.Flush();
        }
    }
}