procedure TForm1.Button1Click(Sender: TObject);
var bmp:TBitmap;
begin
bmp := TBitmap.Create;
bmp.Width := Screen.Width;
bmp.Height := Screen.Height;
BitBlt(bmp.Canvas.Handle, 0,0, Screen.Width, Screen.Height,
GetDC(0), 0,0,SRCCOPY);
Image1.Width := Screen.Width;
Image1.Height := Screen.Height;
Image1.Picture.Assign(bmp);
bmp.Free;
end;