Because PNG and GIF are accepted, what happens if I submit transparent pixels? Do they become black? White? Do end user devices render them transparently with w

Because PNG and GIF are accepted, what happens if I submit transparent pixels? Do they become black? White? Do end user devices render them transparently with window BG behind them? What if the GIF is animated? I feel like Apple left a few fun low-hanging edge cases on the table here. Also no barcodes; but does that include QR codes?