Описание CopyRect

procedure CaptureScreen(ABitmap: TBitmap);
const CAPTUREBLT = $40000000;
var
  hdcScreen: HDC;
  hdcCompatible: HDC;
  hbmScreen: HBITMAP;
begin
  hdcScreen := CreateDC('DISPLAY', nil, nil, nil);
  hdcCompatible := CreateCompatibleDC(hdcScreen);

  hbmScreen := CreateCompatibleBitmap(hdcScreen,
    GetDeviceCaps(hdcScreen, HORZRES),
    GetDeviceCaps(hdcScreen, VERTRES));

  SelectObject(hdcCompatible, hbmScreen);
  ABitmap.Handle := hbmScreen;
  BitBlt(hdcCompatible,
    0, 0,
    ABitmap.Width, ABitmap.Height,
    hdcScreen,
    0, 0,
    SRCCOPY or CAPTUREBLT);

  DeleteDC(hdcScreen);
  DeleteDC(hdcCompatible)
end;

procedure getobl(filename: STRING; l,r,w,h: integer);
var b,b2: tbitmap;
begin
 b := tbitmap.Create;
 b2:= tbitmap.Create;

 b2.Width := w;
 b2.Height:= h;

 CaptureScreen(b);
 b2.Canvas.CopyRect(Rect(0,0,w,h),
                    b.canvas,
                    Rect(l,r,l+w,r+h));

 b2.SaveToFile(filename);
 b.Free; b2.Free
end;

procedure TForm1.SpeedButton2Click(Sender: TObject);
begin
 getobl('1.bmp', 874,618, 150,150) // нач. позиция по x-y и width-height
end;