Flipping images is a nightmare!

[peterbone]

It's very easy to flip a tbitmap horizontally with scanline

for y := 0 to Bitmap.Height - 1 do begin
  LRowIn := Bitmap.Scanline[y];
  LRowOut := BitmapOut.Scanline[y];
  for x := 0 to Bitmap.Width - 1 do begin
     LRowOut[x] := LRowIn[Bitmap.Width - x - 1];
  end;
end;

something like that (not tested).