File:Postcard of the Blackstone of Miami Beach Florida.jpg

This work is in the public domain in the United States because it was published in the United States between 1923 and 1977 without a copyright notice. The card has no copyright markings on it as it can be determined from the link above. United States Copyright Office, Circular 3 states: In general, for works first published before March 1, 1989, the copyright owner was required to place an effective notice on all publicly distributed “visually perceptible” copies. A visually perceptible copy is one that can be seen or read, either directly or with the aid of a machine. Examples of visually perceptible copies include a book, sheet music, a photograph, or film. A visually perceptible copy does not include a CD, a vinyl record, or an .MP3 recording of a literary, dramatic, or musical work. The notice for visually perceptible copies should contain all three elements described below. They should appear together or in close proximity on the copies.

1. The copyright symbol © (or for phonorecords, the symbol ℗); the word “Copyright”; or the abbreviation “Copr.”
2. The year of first publication. If the work is a derivative work or a compilation incorporating previously published material, the year date of first publication of the derivative work or compilation is sufficient. Examples of derivative works are translations or dramatizations; an example of a compilation is an anthology. The year may be omitted when a pictorial, graphic, or sculptural work, with accompanying textual matter, if any, is reproduced in or on greeting cards, postcards, stationery, jewelry, dolls, toys, or useful articles.
3. The name of the copyright owner, an abbreviation by which the name can be recognized, or a generally known alternative designation of owner. Example © 2007 Jane Doe.
4. An effective notice includes three general elements, as described above, as a single continuous statement. It was permissible to omit the year of publication for works reproduced on greeting cards, postcards, stationary, jewelry, dolls, toys, or any useful article.
5. Copyright notice was required for all works first published before March 1, 1989, subject to some exceptions discussed below. If the notice was omitted or a mistake was made in using copyright notice, the work generally lost copyright protection in the United States.
6. Copyright notice is optional for works published on or after March 1, 1989, unpublished works, and foreign works.
7. An omission or mistake in using a copyright notice may not have invalidated the copyright to works published between January 1, 1978 and March 1, 1989.