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My image library has been hit with bitrot, as exemplified by the image below:

enter image description here

This is for a lot of images, maybe 2%, and is of course frustrating. I have backups, but the bitrot is in the backups too. I have a "mostly Apple household", but the backups are mostly Western Digital drives, one of them a "smart" WD "My Cloud Mirror" with an non user accessible file system which I assume doesn't simplify the situation.

I have browsed online but find it hard to come up with a good recovery strategy. Does anyone have experience from recovering from a similar situation? Also, if there is a particular hard drive that is the culprit, what are the best ways to identify this drive? If I can't identify the drive, should I move to a new drive and destroy all the old drives?

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    If the backups are all identically corrupted, that would say the root issue is on the source drive. If they're Time Machine drives, your history may have clean versions. I'd suggest for in future having an air-gapped additional backup that always has a last-known-good status. For files that remain unchanged over time, this would be relatively simple to achieve; whether using something online like Backblaze, or writeable DVDs kept off-site & refreshed to new disks every 5 years or so.
    – Tetsujin
    Oct 25, 2020 at 8:55
  • Based on my own experience; cheap "backup disks" of type "My cloud" and "My book" contain cheap disks which are prone to fail after shorter time than more 'standard' drives; the result is as above. As with anything else, cheap things has limitations. Lost data is irrecoverably lost unless you have a healthy backup. I would say 'bitrot' is more related to old data stored in a format that has been rendered obsolete.
    – Hannu
    Oct 25, 2020 at 11:36
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    @Hannu - bit rot is real, & jpgs are very very prone to it. Wikipedia has a rather terse explanation but it has some jpg examples - en.wikipedia.org/wiki/Data_degradation The fault could be 'cheap' disks, but also copy errors or in this case propagated errors affecting many subsequent backups [which is why you really need incremental backups or safe, known-good data points.]
    – Tetsujin
    Oct 25, 2020 at 16:52
  • I have approximately 40 years of data-related experience, and the only point in time when I experienced this was when I attempted to use cheap drives. I quickly moved away from that and it stopped; I removed the disk from that casing and cautiously used it as an internal drive - the problem did not reappear: So i take the problem was the casing (with a small interconnecting PCB).
    – Hannu
    Oct 25, 2020 at 17:47

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The way to recover from bitrot is to find a copy of the data that doesn't have it.

There is no way to recreate data that no longer exists. The suggestions of cause noted in the comments above are all valid and likely. The fact you're seeing the same degradation on multiple "backups" indicates the problem occurred in the original and so your only hope is to find some backup of that original which is good.

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