I'm working on a specialised archaeological research book, and have a few questions about this.
1. What is the copyright position if I want to use photos and diagrams that are already in the public domain?
2. I engaged (on a simple 'all expenses paid' basis) someone to shoot a number of photographs under my direction. I assume I own the copyright.
3. What is the position if I decide NOT to copyright my book. Can I sell it without redress?
1. Public domain works
Currently, in English law, there are two main senses in which a photograph may be in the public domain. Copyright may have expired, or the copyright owner may have "granted" or "dedicated" the photo to the public domain.
Unless you have expressly agreed otherwise (e.g. in a contract), you are generally free to use and adapt photographs the copyright in which has expired - with or without attribution.
In theory, the public domain dedication is legally problematic. In practice, however, the use of works that have been dedicated to the public domain is, at least, extremely low risk.
2. Commissioned works
No - the photographer as owner will be the first owner of copyright. You should ask the photographer to sign an "assignment of copyright", and possibly a waiver of the moral right to paternity too.
In English law, copyright automatically subsists. There is no process of registration, as there is for example with registered trade marks or patents.
Under the Berne Convention, such formalities are restricted.
In the USA, however, there is a copyright registration procedure, and this can make enforcement of copyright in the USA easier and more lucrative.