C#验证码

    public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Graphics g = this.CreateGraphics();//创建GDI对像

            //创建画笔(颜色)
            Pen npen = new Pen(Brushes.Red);

            //创建两个点
            Point n1 = new Point(20, 20);
            Point n2 = new Point(255, 255);

            g.DrawLine(npen, n1, n2);

        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = this.CreateGraphics();//创建GDI对像

            //创建画笔(颜色)
            Pen npen = new Pen(Brushes.Red);

            //创建两个点
            Point n1 = new Point(20, 20);
            Point n2 = new Point(255, 255);

            g.DrawLine(npen, n1, n2);

        }

        private void button2_Click(object sender, EventArgs e)
        {
            Graphics ng = this.CreateGraphics();

            //创建画笔
            Pen npen = new Pen(Brushes.Red);

            Size sz=new System.Drawing.Size(100,100);
            Rectangle res = new Rectangle(new Point(50, 50), sz);

            ng.DrawRectangle(npen, res);
        }

        private void button3_Click(object sender, EventArgs e)
        {
            Graphics g = this.CreateGraphics();

            Pen npen = new Pen(Brushes.Blue);

            Size sz = new System.Drawing.Size(180, 180);

            Rectangle rec = new Rectangle(new Point(150, 150), sz);

            g.DrawPie(npen, rec, -50, -50);
        }

        private void pictureBox1_DoubleClick(object sender, EventArgs e)
        {
            Random rd = new Random();
            string str = null;

            for (int i = 0; i < 5; i++)
            {
                int n1=rd.Next(1, 10);
                str += n1;    
            }

            Bitmap bmp=new Bitmap(120,40);
            //创建gdi
            Graphics gd = Graphics.FromImage(bmp);

            //画图
            for (int i = 0; i < str.Length; i++)
            {
                Point pt = new Point(i * 20, 0);
                string[] fonts={"微软雅黑","宋体","黑体","隶书","仿宋"};
                Color[] colors={Color.Red,Color.Black,Color.Blue,Color.Orange,Color.Plum};
                gd.DrawString(str[i].ToString(), new Font(fonts[rd.Next(0, 5)], 15, FontStyle.Bold), new SolidBrush(colors[rd.Next(0, 5)]), pt);
            }
            //给图片加线
            for (int i = 0; i < 20; i++)
            {
                Point xpt1 = new Point(rd.Next(0, bmp.Width), rd.Next(0, bmp.Height));
                Point xpt2 = new Point(rd.Next(0, bmp.Width), rd.Next(0, bmp.Height));
                gd.DrawLine(new Pen(Brushes.Red), xpt1, xpt2);
            }

            //给图片加点
            for (int i = 0; i < 50; i++)
            {
                Point p1 = new Point(rd.Next(0, bmp.Width), rd.Next(0, bmp.Height));
                bmp.SetPixel(p1.X, p1.Y, Color.Black);
            }
            //将图片放到pictureBox中
            pictureBox1.Image = bmp;
        }