[NiLuJe]

That said, there's no JFIF, EXIF or 8BIM anywhere in that file, so Kovid's tweaked imghdr doesn't catch it either. To keep false-positives at bay, I tweaked my extra check a bit:

                # imghdr only checks for JFIF or Exif JPEG files. Apparently, there are some with only the magic JPEG bytes out there...
                # ImageMagick handle those, so, do it too.
                if imgtype is None and data[0:2] == b'\xFF\xD8':
                    # Get last non-null bytes
                    last = len(data)
                    while (data[last-1:last] == b'\x00'):
                        last-=1
                    # Be extra safe, check the trailing bytes, too.
                    if data[last-2:last] == b'\xFF\xD9':
                        imgtype = "jpeg"