// Capture a full screen image
        private void btnFullScreen_Click(object sender, EventArgs e)
        {
            // Create an image and save the captured image
            Bitmap image = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);
            Graphics imgGraphics = Graphics.FromImage(image);
            // Set the screenshot area
            imgGraphics.CopyFromScreen(0, 0, 0, 0, new Size(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height));
            // save
            SaveImage(image);
        }
// Save image file
        private void SaveImage(Image image)
        {
            if (saveFileDialog.ShowDialog(this) == DialogResult.OK)
            {
                string fileName = saveFileDialog.FileName;
                string extension = Path.GetExtension(fileName);
                if (extension == ".jpg")
                {
                    image.Save(fileName, ImageFormat.Jpeg);
                }
                else
                {
                    image.Save(fileName, ImageFormat.Bmp);
                }
            }
        }