I want to use a photo I found in an old newspaper in my book but I can’t find the copyright owner and the newspaper is now out of business. How can I determine if it’s in the public domain?

Just because you can’t find the copyright owner doesn’t mean you can use that person’s property for profit. If the work isn’t in the public domain, and if you can’t find the owner, you can’t use it. It’s that simple. The University of North Carolina provides a really nifty chart titled When U.S. Works Pass into the Public Domain:

Note: The information on the site mentions that property of the U.S. government is considered in the public domain. However, some items appearing on government websites and in government publications may have been created by a government contractor. In those cases, the contractor may have retained the copyright. So, never assume you can use something you find on a government website for profit. Some government sites have copyright information on them, which tell you exactly how you can use the material. If they don’t, you must find the copyright owner before using the information/photos.