could the black box be lifted revealing the contents of what it covered
If we’re talking raster images, then no, you’re not using some mathematical model to morph an image, you’re just overwriting pixels arbitrarily, so there would be no way to recover what’s “under” the box because there’s no second layer.
If instead it’s something like a PDF (vector), then placing an object over another without flattening the result would allow you to move it out of the way to reveal what’s under.
I would add, of course, make sure that the black box covers enough to prevent the possibility of inferring what’s under, so if it’s text or other organic things that can be “statistically” regenerated with some model, don’t leave any borders that can identify the item, reconstructed data may be synthetic, but can provide informed guesses







To measure them, actually!