Comment 2 for bug 516763

I don't have exiftran installed nor Ubuntu set up atm. I did glance at the code, however. You could try to replace the offending line
"super(JpegUtility, self).execute(photo)" with

        system.call(utility.get_command_line(self,photo, info['path'],
            self.get_lossless_filename(photo,info)))

and remove that part from the end of the call method. It looks a bit suspicious to me (I expect it should call exiftran/jpegtran only if provided file happens to be a jpeg, no?).

It's also curious that execute method of JpegUtility contains almost exact content as the call method of LossLessSaveUtilityMixin. If you end up doing the above change and it works out ok, you might want to eliminate JpegUtility class altogether. Utility looks like a good candidate for removal as well.