ASP.NET中一个简单的验证码生成程序，留着以后用！

   protected void Page_Load(object sender, EventArgs e)
        {
            this.CreateCode(this.CreateStr());
            Session["check_code"] = CreateStr();
        }
        protected string CreateStr()
        {
            string str = "";
            Random random = new Random();
            str = random.Next(1000,9999).ToString();
            return str;
        }
        protected void CreateCode(string code)
        {
            if (code.Length == 0)
                return;
            Random random = new Random();
            Bitmap map = new Bitmap(4*14,30);//定义一个宽度为4*13,高度为30像素的位图
            Graphics g = Graphics.FromImage(map);
            g.Clear(Color.White);
            g.DrawRectangle(new Pen(Color.Gray), 0, 0, map.Width - 1, map.Height - 1);//进行描边

            //...开始写字
            Matrix matrix;//声明用来操作矩阵的类
            LinearGradientBrush brush = new LinearGradientBrush(new Point(0, 0), new Point(map.Width, map.Height), Color.Red, Color.Green);
            for (int j = 0; j < code.Length; j++)
            {
                string schar = code.Substring(j,1);
                matrix = g.Transform;//获取当前绘图的世界坐标系。
                float shearx = 0.0F;
                float sheary = 0.0F;
                matrix.Shear(shearx,sheary);
                g.Transform = matrix;
                g.DrawString(schar,new Font("黑体",14.0f,FontStyle.Bold),brush,new PointF(0.0f+(13.0f*j),random.Next(30-20)));
            }
            //画干扰线
            int x1=random.Next(map.Width);
            int y1=random.Next(map.Height);
            int x2=random.Next(map.Width);
            int y2=random.Next(map.Height);
            g.DrawLine(new Pen(Color.Black),new Point(x1,y1),new Point(x2,y2));
            //画干扰点
            for(int i=0;i<10;i++)
            {
                map.SetPixel(random.Next(map.Width),random.Next(map.Height),Color.FromArgb(random.Next(255),random.Next(255),random.Next(255)));
            }
            Response.Clear();
            MemoryStream stream=new MemoryStream();
            map.Save(stream,ImageFormat.Gif);
            Response.ContentType="image/Gif";
            Response.BinaryWrite(stream.ToArray());

 

        }