The FITS standard is a container that describes how to store image data and meta-data. Professional tools, from the early age of the FITS format, like ds9 (Harvard Smithsonian Center for Astrophysics), fv (FITS viewer from NASA), store images bottom-up. We might be tempted to say that it does not really matter, but when demosaicing or astrometry is involved, problems arise. For example, the usual RGGB Bayer pattern becomes GBRG if the image is upside-down.