一个生成Validatecode 的代码。

Response.Clear();
            Response.ContentType  =   " image/jpeg " ;
             int  width  =   50 ;
             int  height  =   25 ;
            Bitmap bmp  =   new  Bitmap(width, height, PixelFormat.Format24bppRgb);
            Graphics g  =  Graphics.FromImage(bmp);
            HatchBrush b  =   new  HatchBrush(HatchStyle.Cross, Color.LightGray, Color.WhiteSmoke);
            g.FillRectangle(b,  0 ,  0 , width, height);
            Random r  =   new  Random(Convert.ToInt32(DateTime.Now.Millisecond));
             string  Code  =  r.Next( 1000 ,  9999 ).ToString();
            Session[ " ValidateCode " ]  =  Code;
            g.DrawString(Code,  new  Font( " Arial " ,  10 , FontStyle.Bold), SystemBrushes.WindowText,  10.0F ,  5.0F );
            bmp.Save(Response.OutputStream, ImageFormat.Jpeg);
            b.Dispose();
            g.Dispose();
            bmp.Dispose();
            Response.End();