It's not a derivative work unless additional creative effort is added. Altering the scan to increase the faithfulness of the reproduction is not creative effort--no more than if you edited an OCR scan of a printed work to correct the typos. Nor are mistakes in the reproduction introduced by an automated process creative efforts.
If you intentionally altered the bust to convert the crown into a bundle of hot dogs, that would be a derivative work. No one would care much about it, though, as the original is what's famous, and they would prefer a faithful reproduction of that to anything you might do to your copy to make it uniquely yours.
Similarly, a photograph of a painting that has been digitally retouched to fix the colors is not a derivative work.
You have to intentionally do something to make your copy uniquely distinguishable from the original. It can be anything. Put a hairy mole on David's buttock. Change the Creation of Adam such that the creator is the FSM. Sneak the TARDIS into Starry Night. Replace all the human heads with Kooikerhondje heads in The Anatomy Lesson of Dr. Nicolaes Tulp.
The Utah Teapot digital model is a derivative work of the original physical teapot, because it was scaled vertically by 3/4. That's enough. Were it not for that one difference, you wouldn't be able to tell whether someone copied the digital model directly, or remeasured the parameters of the physical model.
(Note that my opinions on this matter are not necessarily going to match those of judges actually able to decide intellectual property disputes.)
Several courts have already ruled that "slavish copies" are not transformative, and not subject to copyright protection. So your opinion on the prints is probably correct.
If you intentionally altered the bust to convert the crown into a bundle of hot dogs, that would be a derivative work. No one would care much about it, though, as the original is what's famous, and they would prefer a faithful reproduction of that to anything you might do to your copy to make it uniquely yours.
Similarly, a photograph of a painting that has been digitally retouched to fix the colors is not a derivative work.
You have to intentionally do something to make your copy uniquely distinguishable from the original. It can be anything. Put a hairy mole on David's buttock. Change the Creation of Adam such that the creator is the FSM. Sneak the TARDIS into Starry Night. Replace all the human heads with Kooikerhondje heads in The Anatomy Lesson of Dr. Nicolaes Tulp.
The Utah Teapot digital model is a derivative work of the original physical teapot, because it was scaled vertically by 3/4. That's enough. Were it not for that one difference, you wouldn't be able to tell whether someone copied the digital model directly, or remeasured the parameters of the physical model.
(Note that my opinions on this matter are not necessarily going to match those of judges actually able to decide intellectual property disputes.)