One of the things that I love about being a lawyer at the Art Institute is the exposure to a wonderful variety of copyright issues springing from the museum’s diverse collection. An interesting example is Peter Blume’s 1944-48 painting, The Rock.
United States copyright law has several quirks depending on when and where a work was created and published. Until recent decades, artists had to comply with certain “formalities,” or risk losing copyright protection. For example, if a painting was “published” (e.g. in a book or on a poster) prior to 1978, then the artist was supposed to “renew” the copyright term for the work at the Copyright Office during the 28th year following first publication, or the work would fall out of copyright in the United States and into the public domain. Without a good calendar app, few artists remembered these deadlines and renewed their copyrights. In 1992, U.S. copyright law did away with the renewal requirement, but that did not save non-renewed works first published in the United States before 1964, which lost copyright protection 28 years after they were published.
In this day and age, it should go without saying that the foregoing does not constitute legal advice and is offered for your edification and amusement only, with no representations or warranties as to accuracy, etc., etc.