We keep all of our pictures on an external USB hard drive. At least once a month or after a large addition of pictures I back it up to my NAS ~30TB in the basement using rsync. That backup gets sent a few hundred miles away to a server (really, just an ancient, headless desktop running Debian tucked under a family member's desk!) with a large HD (12TB) via Syncthing. Syncthing is set to be one-way, pushing changes from my backup to the remote server only.