Overview
Is a photograph of a public domain work copyrighted?
The short answer is no. The long answer is a bit more considered. To begin with, consider the quote by Wikipedia – ‘The official position taken by the Wikimedia Foundation is that “faithful reproductions of two-dimensional public domain works of art are public domain“. Photographs are considered ‘faithful reproductions’, therefore are considered in the public domain.
Now to qualify the answer above. If someone has taken a straightforward photograph of a piece of art that is public domain, the photo is also considered to be in the public domain. However if the photographer has materially added to the photograph in some way, then it may be considered copyrighted. It has to be significantly changed in some way to be copyrighted, such as extensive lighting or filters, extensive photoshop editing such as changing the background or coloring, or adding elements not originally in the source art, and similar changes. How much change is a matter of judgement.
Finally a copyright notice on a photograph of a public domain piece of artwork may or may not represent its true copyright status. A rule of thumb might be, if there was no copyright on the photo, would anyone be able to tell if the photograph was distinctly different than any other photograph taken of the same piece of artwork? Or can it be traced back to a single individual due to some distinct aspects in the photograph?
What is a 'Collection Copyright?'
(More International copyright information)
Concluding Overview
(More coming soon)