I know that works created by US Government employees in the course of their duties are considered Public Domain in the US, but are they automatically in the public domain internationally as well?
Say, for the purposes of this exercise, I wanted to publish a pamphlet here in Australia about various types of animals commonly seen on TV but not present in Australia. As part of this, I decide use a photograph of a Grizzly Bear taken by an employee of the US National Parks Service and used on an official NPS website as an illustration of a Grizzly Bear. (It goes without saying that the image would have a photo acknowledgement to the NPS, as that’s just basic courtesy).
Is that photograph in the Public Domain here in Australia as well, or could the NPS turn around and say “Hang on, that photograph is copyrighted outside the US and you can’t use it without our permission and/or giving us money”?
In order to enforce a copyright, someone has to claim to be the rights holder. The US is not claiming sole rights, but they are the acknowledged source. As such, anyone else claiming copyright is lying, as you can prove by the date of the US public domain publication.
So a third party can claim anything they like, but they won’t win a claim against you in the fact situation you’ve presented.
Edit - Seems like I misread your question - let me come back and clarify in a following post.
The short answer is no. The Berne Convention states that whatever the copyrightability of a work in one country, has no bearing on the copyrightability of the same work in a different country.
It’s not necessarily in the public domain in Australia just because it is in the US - it would depend on Australian law, which I am not up to date on right now. If I have time I’ll search around for a more definitive answer for you.
Virtually every industrialized country is signatory to the Berne Convention. While the copyright laws of individual countries do vary some in their particulars, and material may fall out of copyright into the public domain in slightly different ways, AFAIK something that is never under copyright in the first place can’t be placed under copyright. Striving to keep materials from having different statuses in different countries is what the Berne Convention is for. That’s why the U.S. lengthened its period of copyright in the 1986 Copyright Act. (Technically to match the European Union, but the ultimate reason was the Berne Convention.)
The U.S. government cannot demand a copyright of its public domain materials just because of its use in another country,