iCloud Photos can help you make the most of the storage space on your iPod touch. When Optimize iPod touch Storage is turned on, all your full‑resolution photos and videos are stored in iCloud in their original formats, with storage-saving versions kept on your iPod touch as space is needed.
Optimize iPod touch Storage is turned on by default. To turn it off, go to Settings 
> [your name] > iCloud > Photos, then tap Optimize iPod touch Storage.
