Public Domain content is free of copyright, but please be aware that if the content of a work contains or depicts any third party intellectual property, such as a background trademark, trade dress, picture, art work, background music or reading, etc., the owner of that intellectual property may have the right to claim that use of the content that infringes the owner's intellectual property rights.
In addition, if the public domain content (in a U.S. government work, for example) contains or depicts the image, voice or other recognizable features of a person, because public domain content generally is not accompanied by model releases, that person may have the right to object to commercial exploitation the content as a violation of their privacy or publicity rights.
For those reasons, any public domain content that contains or depicts any such third party intellectual property or the image, voice or other recognizable features of a person should be considered to be "Editorial Content" - meaning it is generally available for editorial use only.
For more information on how to identify Third Party Rights on public domain content, please watch our "Public Domain 101" video below.
For more information on how to proceed in those cases, read another article from our Help Center article: What Does "Editorial Only" Mean? or Which Files Are Cleared for Commercial Use?