I want to know if the photos are securely deleted. It's not enough that the mere reference to a file is gone. I want everything overwritten with zeroes, and the photo made properly irrecoverable.
They are definitely not. I’m honestly surprised at how many folks here on HN (a presumably tech savvy crowd) think that Instagram (or any tech co) is “writing zeros” when a user hits a delete button.
Always encrypt the data at rest, and delete by deleting the key is likely how this would be done. This way you can also delete e.g. tape backups without actually loading the tape and re-writing the whole thing with certain portions deleted, which is not really practical.
Yes, and you could also queue files for deletion at a later stage by throwing away the encryption key for a large batch of files which have been queued for deletion.
So what if someone sleuths around in the e-waste dept. of Instagram and steals a few hard-drives with literally Terabytes of potentially very sensitive data? That's why I would hope Instagram are encrypting data at rest with something like LUKS.