The Synology mentioned still doesn't provide the best protection. If a bit in a file gets corrupted or flipped, it won't fix that, because it can't. You're still dependent on your backups if a file gets corrupted on your active storage. And if you missed that corruption and continued your normal backups, well, your backups won't save you from that. How fatal is one flipped bit? For a photograph, it can be pretty much totally fatal. It's not like a spot on a photo, since in an image file all spots are dependent on each other. How frequent? That's a function of time... I'm a photographer, and I've had it happen to a few files here and there in my 15 TB of photographs and videos. Thankfully not to any really valuable ones. But, it's happened at a large scale (a few hundred images) in some backups that had issues that weren't detected at the time.
There's a technology called ZFS that DOES protect you from what's commonly called "bit rot" - bits degrading over time due to cosmic ray strikes, disk degradation, things like that. It's an "ultimate" quality solution - there are other ones that preceded ZFS like copy-on-write, and some derivatives of ZFS like Netgear's BTRFS (a variation on C-O-W.) Like many photographers, my ultimate archive is now on ZFS systems, with working files and working archives living on less painful to manage NAS systems.
For scanned photos of family members, protecting against bit rot is the only way to be confident that those images will still be viewable and printable for generations to come. (Assuming they can still read disks... go ahead, try to find a way to access those zip drives that used to be all the rage...)