Bitmap bitmap = new Bitmap(2048, 1024);
Graphics graphic = Graphics.FromImage(bitmap);
//此處使用GDI+在graphic對象上繪圖...
graphic.Dispose();
pictureBoxMain.Image = bitmap;
pictureBoxMain.SizeMode = PictureBoxSizeMode.Zoom;

Image objImage = Image.FromFile(@"../../Resouce/Image/backImage.jpg");
Graphics graphic = Graphics.FromImage(objImage);
//此處使用GDI+在graphic對象上繪圖...
graphic.Dispose();
pictureBoxMain.Image = bitmap;
pictureBoxMain.SizeMode = PictureBoxSizeMode.Zoom;