Orphan works are works that are in-copyright but do not have a contactable copyright holder. They’re tricky and annoying as far as reuse goes because while technically they’re not re-usable without permission, how do you get permission? People have discussed this problem at length, but The University of Michigan’s Copyright office — the people who are working on the copyright review management system — are trying to do something about it. They launched a project to try to track down and identify the rights holders of orphan works created between 1923-1963 in the HathiTrust Digital Library. In doing so, they hope to get a general idea of the scope of the problem and at the same time develop best practices for identifying orphan works. They might also help HT make more of their content available as its copyright status is determined.
I think it was a lamentable misstep when the legislature removed the requirement to apply for copyright extension.