When talking to a copyright attorney about what is in the public domain, you will often get the response "it's complicated". While anything published prior to 1923 is pretty likely to be in the public domain, anything created after 1923 is a bit more complicated.
Making matters even more complex is a recent ruling by US District Court which reiterated that some elements of a copyright created prior to 1923 can live on with further protection. The case involved Sherlock Holmes and the ancillary characters created in the series of novels and stories. While the original character of Sherlock Holmes was first published in 1887, the last 10 stories were published after 1923. The Plaintiff in this case argued that elements of Holmes' character, as well as Watson's character, were established only in the last 10 stories which were published after 1923, and therefore these elements should continue to enjoy copyright protection. The Court agreed with this argument and ruled that certain elements of the Holmes' stories remain protected, such as Holmes' retirement from his detective agency, for the foreseeable future.
For a more in depth look at this case, you can read this article: http://www.hollywoodreporter.com/thr-esq/sherlock-holmes-judge-declares-popular-667755.
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