I haven't done this, but there's an easy way to verify what the case is... If PNGs are just being displayed according to a standard PNG API like libpng or a closed-source equivalent, they are capable of more tricks than a PICT. I believe a PICT even has an animation capability (albeit rarely used). Try one and see what happens. If it shows up as intended, moves, whatever, then it's just displaying the PNG. If not, it's either translating (most likely) or possibly modifying and flattening on the fly (which would be a possibility, but pointless)

I'm the asshole. You wanna be a shit? You gotta go through ME.