And that's just in the non-adversarial simple case.

If you don't know the provenance of images you are putting black box on (for example because of a rogue employee intentionally wanting to leak them, or if the image sensor of your target had been compromised to leak some info by another team), your redaction can be rendered ineffective, as some images can be made uncroppable by construction .

(Self-plug : https://github.com/unrealwill/uncroppable )

And also be aware that compression is hiding everywhere : https://en.wikipedia.org/wiki/Compressed_sensing