A copyrighted work is publicly displayed if the public has access to it.
The right to publicly display or perform a creative work is one of the fundamental rights granted to a copyright holder. A work is publicly displayed or performed if the public can view it. Whether the public has to pay is not an issue.
U.S. Copyright Act, Section 101 states:
“To perform or display a work “publicly” means (1) to perform or display it at a place open to the public or at any place where a substantial number of persons outside of a normal circle of a family and its social acquaintances is gathered; or (2) to transmit or otherwise communicate a performance or display of the work to a place specified by clause (1) or to the public, by means of any device or process, whether the members of the public capable of receiving the performance or display receive it in the same place or in separate places and at the same time or at different times.
So, a painting on the wall of someone’s home is not publicly displayed, but a painting on the wall of City Hall is. When the work in question is an outdoor artwork, or a building, things can become difficult to determine. There is also the question of whether a search engine is publicly displaying works when it shows thumbnail images.