asp.net code to generate English character digital verification codes-practical tips

Copy Code code as follows:

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 ("XXFarEastFont-Arial"), 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));
}
}