For example,
we currently disallow PNG images greater than 12.5 MP.
Are you sure about this? I recall a configurable 12.5 MP limit on rendering
of JPGs, but does that also apply to PNGs? And "disallow" is a bit ambiguous
here. They just won't render / have thumbnails created, they aren't blocked
from being uploaded, no?
It's the other way. JPEGs are scaled, because they are decompressed "in
a pipe" bug pngs are not.
We have pngds program to deal with that, but it was never deployed.