分享一个验证码程序，字母和数字

验证码程序的图片是有1--10张图片，系统自动选择，是字母和数字一起的一个验证码。很不错的。拿出来和大家分享一下。

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;

public partial class Ajax_Login_Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!this.IsPostBack)
{
this.GenImg(this.GetCode(4));
}
}
//产生随机字符串
private string GetCode(int num)
{
string[] source ={ "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z" };
string code = "";
Random rd = new Random();
for (int i = 0; i < num; i++)
{
code += source[rd.Next(0, source.Length)];
}
return code;
}

//生成图片
private void GenImg(string code)
{
Random rd = new Random();
Bitmap myPalette = new Bitmap(120, 60); //定义一个画板
Graphics gh = Graphics.FromImage(myPalette); //在画板上定义绘图的实例
Rectangle rc = new Rectangle(0, 0, 120, 60); //定义一个矩形
String picPath = Server.MapPath("pic/bg" + rd.Next(1, 4).ToString().Trim() + ".jpg");
Bitmap imagefile = (Bitmap)System.Drawing.Image.FromFile(picPath, true); //得到一张位图
TextureBrush texture = new TextureBrush(imagefile); //以图片建立绘图刷
Color[] fontcolor = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Red, Color.Brown, Color.DarkCyan, Color.Purple }; //定义 8 种颜色
String[] fontname = { "Verdana", "System", "Comic Sans MS", "Arial", "宋体" }; //定义 5 种字体
Font myfont; //字体定义
SolidBrush mybrush; //画笔定义

gh.FillRectangle(texture, rc);//使用绘图刷填充矩形，到此得到图片背景

for (short i = 0; i <= code.Length - 1; i++)
{
myfont = new Font(fontname[rd.Next(0, 5)], 30, FontStyle.Italic); //随机字体,42号，斜体
mybrush = new SolidBrush(fontcolor[rd.Next(0, 8)]); //随机颜色
gh.DrawString(code.Substring(i, 1), myfont, mybrush, 3 + (i * 23), rd.Next(1, 8));//在矩形内画出字符串
}

myPalette.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);//将图片显示出来

Session["ValidateCode"] = code;//将字符串保存到Session中，以便需要时进行验证

gh.Dispose();
myPalette.Dispose();
}
}