Copyright protects original works (works that reflect the author’s own intellectual creation), which among other things include literary works, dramatic works, art or films.
Some creations that do not meet the originality criteria, such as non-original photographs, non-original databases, or the recording of a phonogram, are also entitled to some rights in certain countries, with a shorter duration of protection. They consist of a copyright-type of protection and are called neighbouring and sui generis rights.
Among other things, copyright does not protect:
Works whose copyright term has expired
Content that does not meet the originality threshold
Ideas (copyright only protects their expression)
Natural artefacts (flowers, rocks, trees, songs of birds)
Mathematical problems and formulas
Governmental, legal and/or judicial documentation, under many legislations.
This is important as it means that not everything that sits in the collections of an archive, library or museum is subject to copyright protection. There is an 'originality' threshold that needs to be met. This is a rather difficult assessment to make, and the only person who can definitively confirm, from a copyright perspective, whether something is original or not, is a judge. Unfortunately, to be on the 'safe side', this results in a tendency by culture heritage institutions to consider most things sufficiently original, and therefore copyright-protected, even though they might not be.