首先我们确定此功能的原理：

1:mousedown事件中记录下起始位置，并且描绘一个虚线边框。
2:mouseup事件中记录下结束位置
3:于是得到一个矩形区域,
4:在目标对象中,DrawImage,其中source为第一个picturebox的图像,起始点,宽度高度换算下.

首先放置两个个图片框pictureBox1和pictureBox2。

        private int _x, _y;
        Image _img = null;
        private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            _img = pictureBox1.Image.Clone() as Image;
            _x = e.X;
            _y = e.Y;

        }

        sender, MouseEventArgs e)
        {
            int sx = _x < e.X ? _x : e.X;
            ? _y : e.Y;
            = Math.Abs(_x - e.X);
            - e.Y);
            Bitmap bmp Bitmap(w, h);
            Graphics g = Graphics.FromImage(bmp);
            g.DrawImage(pictureBox1.Image, 0, 0, w, h), sx, sy, w, h, GraphicsUnit.Pixel);
            g.Save();
            pictureBox2.Image = bmp;
            bmp.Save("c:\\" + DateTime.Now.Ticks.ToString() + ".jpg", System.Drawing.Imaging.ImageFormat.Jpeg);
        }

        sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                Pen p 1);
                p.DashStyle = System.Drawing.Drawing2D.DashStyle.Dash;
                Graphics g = Graphics.FromHwnd(pictureBox1.Handle);
                < e.X ? _x : e.X;
                ? _y : e.Y;
                - e.X);
                - e.Y);
                pictureBox1.Image = _img;
                g.DrawRectangle(p, sx, sy, w, h);
            }
        }int h = Math.Abs(_y int w = Math.Abs(_x int sy = _y < e.Y int sx = _x = new Pen(Color.Red, private void pictureBox1_MouseMove(objectnew Rectangle(= newint h = Math.Abs(_y int w int sy = _y < e.Y private void pictureBox1_MouseUp(object

此段代码实现的截图功能算是比较完善，在拖拽鼠标时，会有一个虚线框方便划分区域。同时，截图可以保存为jpeg格式的图片。