asp.net 验证码 实现

第1种.
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.Imaging;
using System.Drawing.Drawing2D;
using System.Drawing;
public partial class fetchcode : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
Random rd = new Random(); //创建随机数对象
//以下4行,产生由6个字母和数字组成的一个字符串
string str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789我你他";
string my51aspx = "";
for (int i = 0; i < 4; i++)
{
my51aspx = my51aspx + str.Substring(rd.Next(39), 1);
}
//验证码值存放到Session中用来比较
Session["Valid"] = my51aspx;
//以下三句,通过随机找一个现有图象产生一个画布Bitmap
string bgFilePath = Server.MapPath(".\\images\\bg" + new Random().Next(5) + ".jpg");//随机找个图象
// string bgFilePath = Server.MapPath(".\\images\\bg2" + ".jpg");//随机找个图象
System.Drawing.Image imgObj = System.Drawing.Image.fromFile(bgFilePath);
Bitmap newBitmap = new Bitmap(imgObj, 90, 30);//建立位图对象
Graphics g = Graphics.fromImage(newBitmap);//根据上面创建的位图对象创建绘图面
Color[] fore = { Color.Black ,Color.Red};
SolidBrush brush = new SolidBrush(fore[new Random().Next(2)]);//设置画笔颜色
//定义一个含10种字体的数组
String[] fontFamily = { "Arial", "Verdana", "Comic Sans MS", "Impact", "Haettenschweiler", "Lucida Sans Unicode", "Garamond", "Courier New", "Book Antiqua", "Arial Narrow" };
//通过循环,绘制每个字符,
for (int a = 0; a < my51aspx.Length; a++)
{
Font textFont = new Font(fontFamily[rd.Next(9)], 15, FontStyle.Regular);//字体随机,字号大小10,加粗
//每次循环绘制