At this point, assume any data that touched an internet connected device is sitting somewhere you don't want it to be.
I think a lot of people are uploading private pictures to the Internet without even being aware of it because of how tricky and sneaky companies are being, nudging you to Cloud-ify everything without explaining clearly that "Cloud" ultimately means "Posted to someone else's computer."
The other half of the story is data loss. Will the files still be there if you leave them alone for a day or a year? Who knows?? Will they really be gone if you delete them? There's literally no way to tell!
The issue in TFA is probably different. If files are only marked for deletion and their data never overwritten, it's conceivable they might show up again after a buggy update.
Of course, one would assume iOS would actually delete the data of files marked for deletion after some expiry, but it's also possible this wasn't happening.
Overwrite with zeros is generally not done as default in flash memories to improve disk life, flash memories have a limited number of times they can be written too, so most memory controllers will try to distribute writes
This seems less a OS bug, more likely iOS/iCloud had a bug on marking deletion correctly
Two potential issues when relying on flash erasure for privacy, neither of which apply to a full device wipe:
1. Filesystem allocation units are almost always smaller than flash erase blocks; erasing and rewriting, e.g., a 1MB flash block whenever a single 4 kB allocation unit it contains is freed will lead to performance and endurance problems.
2. On desktop and laptop systems, erase (ATA TRIM/SCSI UNMAP/NVMe Deallocate) operations are typically deferred to a low-priority or periodic background task for performance reasons; the same may apply to iOS devices.
In the case of full device wipes on modern Apple devices (iOS and Apple Silicon Mac), this is mostly moot anyway from a privacy perspective, because encrypted storage makes data effectively unreadable as soon as encryption keys are wiped.
Either way, horrible day for Apple's "Privacy First" charade.
I wish I could find the video I uploaded to YouTube when me and my friends were kids. I deleted it out of embarrassment when I was older but it was so funny. (Video involved us getting shocked by a CRTs capacitor on camera).
1. “Sync to iCloud” is enabled in Photos
2. You take a screenshot, it saves to photos, it syncs to iCloud
3. You delete the screenshot from Photos
…is there still a copy in iCloud? Maybe…
While the data may technically remain, unless the storage medium explicitly specifies otherwise (like E.G. snapshotting filesystems), "deleting" does often imply immediately overwriting enough metadata that it probably shouldn't be possible for the files to be trivially/accidentally resurfaced by a bug.