uses jpeg;

procedure TForm1.Button1Click(Sender: TObject);
var ImageJPEG : TJPEGImage;
 ImageBMP : TBitmap;

begin
 if OpenPictureDialog1.Execute then
 begin
 ImageBMP := TBitmap.Create;
 try
 ImageBMP.LoadFromFile(OpenPictureDialog1.FileName);
 ImageJPEG := TJPEGImage.Create;
 try
 ImageJPEG.CompressionQuality:=50;
 ImageJPEG.Assign(ImageBMP);
 if SavePictureDialog1.Execute then
 ImageJPEG.SaveToFile(SavePictureDialog1.FileName);
 finally
 ImageJPEG.Free;
 end;
 finally
 ImageBMP.Free;
 end;
 end;
end;

procedure TForm1.Button2Click(Sender: TObject);
var
 ImageJPEG : TJPEGImage;
 ImageBMP : TBitmap;

begin
 if OpenPictureDialog1.Execute then
 begin
 ImageJPEG := TJPEGImage.Create;
 try
 ImageJPEG.LoadFromFile(OpenPictureDialog1.FileName);
 ImageBMP := TBitmap.Create;
 try
 ImageBMP.Width := ImageJPEG.Width;
 ImageBMP.Height := ImageJPEG.Height;
 ImageBMP.Canvas.Draw(0,0,ImageJPEG);
 if SavePictureDialog1.Execute then
 ImageBMP.SaveToFile(SavePictureDialog1.FileName);
 finally
 ImageBMP.Free;
 end;
 finally
 ImageJPEG.Free;
 end;
 end;
end.