[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool GetWindowRect(IntPtr hWnd, out RECT lpRect);

[StructLayout(LayoutKind.Sequential)]
public struct RECT
{
    public int Left;
    public int Top;
    public int Right;
    public int Bottom;
}

private void cmdOptions_Click(object sender, EventArgs e)
{
RECT rct;
HandleRef lcHnd = new HandleRef(this, this.Handle);
if (!GetWindowRect((IntPtr)lcHnd, out rct))
{
    MessageBox.Show("ERROR");
}
else
{
    int windowWidth = System.Math.Abs(rct.Right - rct.Left);
    int windowHeight = System.Math.Abs(rct.Bottom - rct.Top);
    System.Drawing.Bitmap currBMP = new Bitmap(windowWidth, windowHeight);
    currBMP = CaptureClip(rct.Left,rct.Top, windowWidth, windowHeight);
                currBMP.Save("C:\\OCRSDK\\CaptBMP.bmp");
}
}

public static System.Drawing.Bitmap CaptureClip(int x, int y, int width, int height)
{
    System.Drawing.Bitmap BMP = new Bitmap(width, height,
                                           System.Drawing.Imaging.PixelFormat.Format32bppArgb);
    System.Drawing.Graphics GFX = System.Drawing.Graphics.FromImage(BMP);
    GFX.CopyFromScreen (x, y, 0, 0, new Size(width, height),
                        System.Drawing.CopyPixelOperation.SourceCopy);
    
    return BMP;            
}