procedure CaptureScreen(AFileName: string);
const
CAPTUREBLT = $40000000;
var
hdcScreen: HDC;
hdcCompatible: HDC;
bmp: TBitmap;
hbmScreen: HBITMAP;
begin
// Create a normal DC and a memory DC for the entire screen. The
// normal DC provides a "snapshot" of the screen contents. The
// memory DC keeps a copy of this "snapshot" in the associated
// bitmap.
hdcScreen := CreateDC('DISPLAY', nil, nil, nil);
hdcCompatible := CreateCompatibleDC(hdcScreen);
// Create a compatible bitmap for hdcScreen.
hbmScreen := CreateCompatibleBitmap(hdcScreen,
GetDeviceCaps(hdcScreen, HORZRES),
GetDeviceCaps(hdcScreen, VERTRES));
// Select the bitmaps into the compatible DC.
SelectObject(hdcCompatible, hbmScreen);
bmp := TBitmap.Create;
bmp.Handle := hbmScreen;
BitBlt(hdcCompatible,
0, 0,
bmp.Width, bmp.Height,
hdcScreen,
0, 0,
SRCCOPY or CAPTUREBLT);
bmp.SaveToFile(AFileName);
bmp.Free;
DeleteDC(hdcScreen);
DeleteDC(hdcCompatible);
end;