Public Domain
Published or translated before 1926
Published by a governmental body or organization (.gov) – Example: https://www.cdc.gov
Available online and denoted by a Creative Commons license
Copyright-free items that have been released to the public domain
Not in the public domain
Published or translated after 1926
Published by a government-adjacent organization (.org) – Example: https://www.wfpha.org (An easy way to confirm this source is not in the public domain is that their website states “© World Federation of Public Health Associations” at the bottom.)
Available online, but without any sort of Creative Commons license
Royalty-free items such as clip art