验证码

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.IO;
using System.Drawing.Imaging;
using System.Drawing;
public partial class Image : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        string tmp = RndNum(Convert.ToInt16(6));
        Session["verify"] = tmp;
        ValidateCode(tmp);
    }
    private void ValidateCode(string VNum)
    {
        Bitmap Img = null;
        Graphics g = null;
        MemoryStream ms = null;
        int gheight = VNum.Length * 9;
        Img = new Bitmap(gheight, 18);
        g = Graphics.FromImage(Img);
        //背景颜色
        g.Clear(Color.WhiteSmoke);
        //文字字体
        Font f = new Font("Tahoma", 9);
        //文字颜色
        SolidBrush s = new SolidBrush(Color.Red);
        g.DrawString(VNum, f, s, 3, 3);
        ms = new MemoryStream();
        Img.Save(ms, ImageFormat.Jpeg);
        Response.ClearContent();
        Response.ContentType = "image/Jpeg";
        Response.BinaryWrite(ms.ToArray());
        g.Dispose();
        Img.Dispose();
        Response.End();
    }
    private string RndNum(int VcodeNum)
    {
        string MaxNum = "";
        string MinNum = "";
        for (int i = 0; i < 5; i++)//这里的4是验证码的位数
        {
            MaxNum = MaxNum + "5";
        }
        MinNum = MaxNum.Remove(0, 1);
        Random rd = new Random();
        string VNum = Convert.ToString(rd.Next(Convert.ToInt32(MinNum), Convert.ToInt32(MaxNum)));
        return VNum;
    }
}