Convertir de BMP a JPG y viceversa
 

Uses JPEG;

Convertir a JPG

Código Delphi [-]
procedure TForm1.Button1Click(Sender: TObject);
var
  MyJPEG : TJPEGImage;
  MyBMP  : TBitmap;
begin
  MyBMP := TBitmap.Create;
  with MyBMP do
  try
    LoadFromFile('A.BMP');
    MyJPEG := TJPEGImage.Create;
    with MyJPEG do
        begin
            Assign(MyBMP);
            SaveToFile('A.JPEG');
            Free;
        end;
   finally
      Free;
   end;
end;

Convertir a BMP

Código Delphi [-]
procedure TForm1.Button2Click(Sender: TObject);
var
  MyJPEG : TJPEGImage;
  MyBMP  : TBitmap;
begin
  MyJPEG := TJPEGImage.Create;
  with MyJPEG do
     begin
         LoadFromFile('A.JPEG');
         MyBMP := TBitmap.Create;
         with MyBMP do
            begin
                Width := MyJPEG.Width;
                Height := MyJPEG.Height;
                Canvas.Draw(0,0,MyJPEG);
        SaveToFile('A.BMP');
                Free;
             end;
         Free;
     end;
end;