The Getty museum used to do that (and be very aggressive about anyone using the old images) until recently. They have since pulled their collective heads out of their collective asses and allowed public access and relatively free use. Other museums still do this kind of senseless protective stuff regularly.
The reproduction itself is still a protected work, but you are free to reproduce the content if you copy it from the original or a reproduction that is no longer protected (i.e. older than 50 years in most jurisdictions I know about).
I don't believe so. INAL but if the photograph attempts to exactly replicate an image I'm pretty sure copyright doesn't hold. So like, a high resolution image of a Caravaggio is still usable as public domain.[0]
I'm pretty sure the Vatican's got to "ruin" the images with a watermark or anyone would be able to use them as is for whatever they want. It'd be different if it was sculpture, but these pics seem to me like they'd definitely fall into the "slavish reproduction of a public domain work" category.
Er, why are we looking at reference on US copyright law here? The State of Vatican City is not a US jurisdiction, and it has its own copyright law (which incorporates, to the extent that it is not preempted by the special laws promulgated by the Vatican, the copyright law of Italy.)
It is debateable whether or not scanning a public domain book allows you to claim copyright on it. Alas.
Some of the early maps of Ireland (from 1840s) have been scanning and rectified and put online by the Ordenance Survey of Ireland. But they're all copyrighted by them, and you can't have them. (they're viewable here http://maps.osi.ie/ )
These should all be public domain. Is there anyone besides Google and the Vatican that watermark public domain works?