def preprocess_file(name, content, PIL_filter=Image.BILINEAR):
        """
        Preprocess files before storing. E.g: optimizing images
        """
        #full_path = self.path(name)
        #content.close()
        start = datetime.datetime.now()
        type_guesser = magic.Magic()

        if not content:
            return content

        content.seek(0)
        type_guessed = type_guesser.from_buffer(content.read(1024))

        logger.debug('Filetype guessed: "%s"' % type_guessed)
        if type_guessed.upper().startswith('JPEG IMAGE'): # Optimize via jpegoptim + jpegtran
            logger.debug('Preprocessing as JPEG image.')
            sh = Sh()

            ## 1st step: shrink to up to 1920x1920px (2 to 4 megapixels)
            inner_start = datetime.datetime.now()
            max_size = 1920 # px
            content.seek(0)
            im = Image.open(content)
            if any([size > max_size for size in im.size]):
                new_content_stream = StringIO.StringIO()
                #im.thumbnail([max_size, max_size], Image.ANTIALIAS) # 2.9 sec
                #im.thumbnail([max_size, max_size], Image.BICUBIC) # 1.6 sec
                #im.thumbnail([max_size, max_size], Image.BILINEAR) # 0.9 sec
                #im.thumbnail([max_size, max_size], Image.NEAREST) # 0.7 sec
                im.thumbnail([max_size, max_size], PIL_filter)
                im.save(new_content_stream, format='JPEG')
                new_content_stream.seek(0)
                new_content = ContentFile(new_content_stream.read())
                new_content.name = content.name
                content = new_content
            inner_finish = datetime.datetime.now()
            logger.debug('Preprocessed: shrinked to %sx%spx via PIL in %s' % (im.size[0], im.size[1], unicode(inner_finish-inner_start)))
            ##

            # Prepare to use *nix system tools from shell
            content.seek(0)
            temporary_file = tempfile.NamedTemporaryFile()
            temporary_file.write(content.read())
            temporary_file.flush()

            ## 2nd step: optimize it
            inner_start = datetime.datetime.now()
            returncode, stdout, stderr = sh.jpegoptim('--preserve', temporary_file.name)
            inner_finish = datetime.datetime.now()
            stdout = stdout.split('\n')[0]
            logger.debug('Preprocessed: size optimized via "jpegoptim" in %s : "%s"' % (unicode(inner_finish-inner_start), stdout))
            ##

            ## 3rd step: convert to progressive if file size > 10kb
            if os.path.getsize(temporary_file.name) > 10240: # 10 kilobytes = 10240 bytes
                inner_start = datetime.datetime.now()
                returncode, stdout, stderr = sh.jpegtran('-copy all -progressive -outfile', temporary_file.name, temporary_file.name)
                inner_finish = datetime.datetime.now()
                logger.debug('Preprocessed: >10kb file got progressive via "jpegtran" in %s' % unicode(inner_finish-inner_start))
            ##

            preprocessed = File(open(temporary_file.name))

        else:
            logger.debug('Not preprocessing this file.')
            preprocessed = content

        if content == preprocessed:
            new_content = content
        else:
            preprocessed.seek(0)
            new_content = ContentFile(preprocessed.read())
            new_content.name = content.name
            preprocessed.close()
            finish = datetime.datetime.now()
            logger.debug('Time spent preprocessing: %s' % unicode(finish-start))

        return new_content