var
  R: TRect;
  P1: TPoint;
  P2: TPoint;
begin
  P1 := Point(10, 10);
  P2 := Point(-10, -10);
  // the third boolean parameter ensures the rectangle to be normalized
  R := TRect.Create(P1, P2, True);
  // here you can query for the rectangle's Height (but I guess that when having this normalized rectangle
  // you won't need it anymore, because this is the rectangle that you can use for cropping)
  ShowMessage(Format('Height: %d', [R.Height]));
end;