ASP.NET验证码

using System;
using System.Collections.Generic;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing;
public partial class Verify : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Random random = new Random();
        int RadNum = random.Next(1000, 10000);
        Session["Verifycode"] = RadNum.ToString();

        Bitmap image = new Bitmap(40, 16);
        Graphics g = Graphics.FromImage(image);

        g.Clear(Color.White);
        //绘制验证码
        g.DrawString(RadNum.ToString(), new Font("黑体", 12), new SolidBrush(Color.Black), 0, 0);
        //绘制杂色
        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()));
        }
        //绘制划痕
        for (int i = 0; i < 2; i++)
        {
            int x1 = random.Next(image.Width);
            int y1 = random.Next(image.Height);

            int x2 = random.Next(image.Width);
            int y2 = random.Next(image.Height);
            g.DrawLine(new Pen(Color.Black), x1, y1, x2, y2);
        }
        image.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Gif);
    }
}

Verify.aspx页面里面写着绘制的图形。

<img id="imgCode" onclick="src='/verify.aspx?s='+Math.random()" src="/verify.aspx"/>
html页面中用来显示验证码的地方