The seminal Supreme Court case on the idea/expression dichotomy in copyright is:

Which of the following can never be copyrighted?

The government can:

Frank grew up in New York and knows a great deal about the city's history. When he retired in 1985, he began collecting old photographs of various parts of the city (these were public domain pictures, meaning nobody claimed copyright ownership and anyone could use them). By 1990, he had a large collection of these photographs, which he began pasting in a book along with captions and short stories. One day his snoopy landlord sneaks in to Frank's apartment and, upon seeing the book, decides to use Frank's organization and captions to write his own book. The landlord's book would: