When Does a Copyright Expire?

"This question is aimed at the duration of copyright. People often want to use a photo or some other copyrighted work, and wonder how they can be sure the copyright has expired. When a copyright expires, material can be lawfully copied.

The current law is that copyright lasts the life of the author plus 70 years. But a copyrighted is subject to the law that is in effect at the time it was created, and the laws have changed over the years."

Here is a chart from Patent Pending that summarizes the duration of copyright for various works based on their dates of creation.