This United States postage stamp was published prior to 1978 and is therefore in the public domain in the United States. See Commons:Hirtle chart for further explanation. Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (50 p.m.a.), Mainland China (50 p.m.a., not Hong Kong or Macao), Germany (70 p.m.a.), Mexico (100 p.m.a.), Switzerland (70 p.m.a.), and other countries with individual treaties.
This image of simple geometry is ineligible for copyright and therefore in the public domain, because it consists entirely of information that is common property and contains no original authorship.
Heptagon
Captions
Photo by me of a letter sent to my father who died in 1980; airmail 1940 censored cover from US to UK, paid 30¢