Public domain images are typically images for which the copyright has expired. It is not easy to determine if an image is in the public domain, especially because copyright laws vary from country to country. For example, a copyrighted work in the United States is protected for the duration
of the artist’s life plus 70 years. Generally, upon the expiration
of this term, the work then falls into the public domain. In contrast, a copyrighted work created in Belarus is protected for the author’s life plus 50 years.
Unfortunately, researching and verifying the copyright status
of public domain images is not practical as part
of our review process. Presently we are enforcing our standing contributor guidelines, which state: "Public domain content cannot
be submitted under any circumstances. If you do not have complete rights to the content, you may not submit it."
There is, however, one small exception to this policy. If you submit images that incorporate NASA elements that are in the public domain, Shutterstock may accept the image as long as the following text is included in the title for that image: “Elements
of this image furnished by NASA.”
https://www.shutterstock.com/contrib...at02/000006554