英文、数字的验证码

using System;
using System.Data;
using System.Configuration;
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.Drawing2D;

public partial class _Default :
System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs
e)
{

Bitmap bmp = new Bitmap(50, 25);
Graphics g =
Graphics.FromImage(bmp);
SolidBrush sb = new SolidBrush(getColor());

g.DrawString(CheckNumber(), new Font("宋体", 16), sb, 0, 0);

bmp.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Gif);


}
public static string CheckNumber()
{
string checkcode =
"abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
int len =
4;
string tmpstr = "";
int iRandNum;
Random rnd = new Random();

for (int i = 0; i < len; i++)
{
iRandNum =
rnd.Next(checkcode.Length);
tmpstr += checkcode[iRandNum];
}
return
tmpstr;
}
private Color getColor()
{
Random r = new Random();

return Color.FromArgb(r.Next(256), r.Next(256), r.Next(256));
}
}