This 1945 United States Federal Security Agency poster for nursing education is an example of a public domain item. Anyone can reproduce and use it. Click on the picture for a larger version. (200 Saint Xavier students went through the program.)
The image is courtesy of Northwestern University's digital collections.
A public domain work is a creative work that is not protected by copyright, and may be freely used by everyone. Works fall into the public domain for three main reasons:
1. the term of copyright for the work has expired,
2. the author failed to satisfy statutory formalities to perfect the copyright or,
3. the work is of the U.S. Government.
As a rule, most works enter the public domain due to age. This includes any work published in the United States before 1923. Other works in the public domain were published before 1964, and the copyright was not renewed. (Renewal was a requirement for works published before 1978.) A smaller group of works in the public domain were published without copyright notice. (Copyright notice was necessary for works published in the United States before March 1, 1989.)
Use the very neat Copyright Slider Tool to determine is a work is still protected by copyright.