int width = Screen.PrimaryScreen.Bounds.Width;
int height = Screen.PrimaryScreen.Bounds.Height;
Bitmap bmp = new Bitmap(width, height);
using (Graphics g = Graphics.FromImage(bmp))
{
g.CopyFromScreen(0, 0, 0, 0, new Size(width, height));
}
bmp.Save(@"c:\1.jpg");
bmp.Dispose();