But why would you upload them in .png? That's such a waste … you could have like 6-8 times the amount of pictures still in high quality (~2000x2000px) … like 600-800 KB per picture instead of like ~4 MB like you have right now (if all your 1200 items have 2 picture attached to them). If you want to keep them for alpha channels or later editing etc. just keep the pngs in a folder on your system and upload compressed images then delete them.
Besides expansion of storage space there could be the route to allow newer file types instead of jpg that have a better compression without much loss in picture quality.