The eighth and ninth lines in our image caption example read "© Heirs of Josephine N. Hopper, Licensed by the Whitney Museum of American Art." This tells us two things.
First, the heirs - and only the heirs - of Josephine N. Hopper hold the copyright to Soir Bleu. Second, the heirs or their legal representative(s) have granted the Whitney Museum of American Art licensing rights to reproduce Soir Bleu. In this case, an image of the painting was made available to print and digital media sources for publicity purposes surrounding an Edward Hopper exhibition.
As was previously stated, nine times out of ten any museum that holds a work also holds the copyright to images of the work. So the museum information line is often also the singular copyright line, and will contain a "©" symbol.
The big exception to this rule - evident in our example image caption here - occurs whenever the artist was active in the 20th Century. Because copyright laws in favor of artists have been greatly stiffened in the past four decades, it is now common for an artist or an artist's estate to hold a work's copyright for 70 years (renewable).
This caption shows the heirs and the Whitney Museum as righteous copyright users. Many other captions accompanying the works of Modern and Contemporary artists will list the artist or the artist's estate as the copyright holder, followed by an overseeing licensing agency and possibly even a Foundation. An example of this would be:
- © 2006 Marcel Duchamp / Artists Rights Society (ARS), New York / ADAGP, Paris / Succession Marcel Duchamp
What this is saying is that four separate legal entities are concerned with clearing copyright permissions.
What I am saying is that it's always a great idea to pay attention to the "©" symbol, no matter how often it appears in an image caption. It's there for good reason.