I'm considering to use Google Photos as primary storage for my photos, because I use multiple devices, and it makes sense to use centralized cloud service.
I really don't like an idea to have have by photos stored only at one place. And, I want to have local backups of my photos (on external HDD).
Downloading few GBs of same photos regularly doesn't make much sense. Therefore I consider to make incremental regular backups (photos uploaded in past N-days/N-weeks), and only occasionally full backups.
Requirements – supported platforms: both Windows and Linux, or directly from web (no native application, works on all platforms)
Best Answer
EDIT: The OP updated that he's working with Linux. Keeping it for Windows users that will arrive here.
For Windows, there's the Google Photos Backup Tool
It would sync your photos and can be set to sync the photos in high or original quality.