<%@ Page Language="C#" ContentType="text/html" ResponseEncoding="utf-8"  Debug="true" %>
<%@ import namespace="System"%>
<%@ import namespace="System.IO"%>
<%@ import namespace="System.Drawing"%>
<%@ import namespace="System.Drawing.Imaging"%>
 
 private void Page_Load(object sender, System.EventArgs e){
 ValidateCode( RndNum(6) );;//测试
 }

 private void ValidateCode(string VNum) {
 Bitmap Img = null;
 Graphics g = null ;
 MemoryStream ms = null ;

 int gheight = VNum.Length*12;
 Img = new Bitmap(gheight,20);
 g = Graphics.FromImage(Img);
 Font f = new Font( "新宋体",12 );
 Solidbrush s = new SolidBrush( Color.Red );
 g.DrawString(VNum,f,s,3,3);
 ms=new MemoryStream();
 Img.Save(ms,ImageFormat.Png);
 Response.ClearContent() ;//更改http ContentType
 Response.ContentType="image/Png";
 Response.BinaryWrite(ms.ToArray());
 //回收资源
  g.Dispose();
 Img.Dispose();
 Response.End();
 }
 private string RndNum(int VcodeNum) {
 string Vchar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,W,X,Y,Z" ;
 string[] VcArray = Vchar.Split(',') ;
 string  VNum = "" ;//由于字符串很短，就不用StringBuilder了
 int temp = -1 ;//记录上次随机数值，尽量避免生产几个一样的随机数

 //采用一个简单的算法以保证生成随机数的不同
 Random rand =new Random();
 for ( int i = 1 ; i < VcodeNum+1 ; i++ ) { 
 if ( temp != -1) {
 rand =new Random(i*temp*unchecked((int)DateTime.Now.Ticks));
 } 
 int t =  rand.Next(35) ;
 if (temp != -1 && temp == t) {
 return RndNum( VcodeNum );
 }
 temp = t  ;
 VNum += VcArray[t];

 }
 return VNum ;
 }