Prior to 1978, the following was required for copyright protection (see United States Copyright Office page 2):

"Visually Perceptible Copies 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 symbol © (letter C in a circle); 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.1 Example © 2007 Jane Doe.")

Carefully studying the front and back scans of this vintage image, which are included in the file history and the source link, show no evidence of #1. It was therefore never under copyright.

Este archivo se encuentra en el dominio público en los Estados Unidos porque fue publicado en ese país entre los años 1931 y 1977 (ambos incluidos) sin haber indicado un aviso de derechos de autor. A menos que su autor haya fallecido años antes, se mantiene bajo propiedad intelectual en los países o zonas que no aplican la regla del plazo más corto para las obras estadounidenses, como China continental (50 años p.m.a., a excepción de Hong Kong o Macao), Alemania (70), Canadá (70), Suiza (70), México (100) y otros países con reglas particulares. Vea esta página y este diagrama como referencia e información. العربية ∙ беларуская (тарашкевіца) ∙ čeština ∙ Deutsch ∙ Ελληνικά ∙ English ∙ español ∙ فارسی ∙ français ∙ Bahasa Indonesia ∙ italiano ∙ 日本語 ∙ 한국어 ∙ македонски ∙ Nederlands ∙ português ∙ русский ∙ sicilianu ∙ slovenščina ∙ ไทย ∙ Tiếng Việt ∙ 中文（简体） ∙ 中文（繁體） ∙ +/−