利用Graphics的截图功能CopyFromScreen

该方式是直接对屏幕进行截图操作

UserControl chartContainPanel = new UserControl();
Graphics graph = chartContainPanel.CreateGraphics();
Size s = chartContainPanel.Size;
Bitmap memoryImage = new Bitmap(s.Width, s.Height, graph);
Graphics memoryGraphics = Graphics.FromImage(memoryImage);
Point screen = chartContainPanel.PointToScreen(this.Location);

// 拷贝屏幕对应区域为 memoryGraphics 的 BitMap  
memoryGraphics.CopyFromScreen(screen.X, screen.Y, 0, 0, s);
memoryImage.Save(fileName);

来源：https://www.cnblogs.com/snsnetw/p/12366062.html