@user6726 does a great job of accurately answering your other questions, but doesn't really answer this one.
For context, there is an exhibition of Banksy works in Moscow, which
apparently was organised without Banksy's consent. Trying to
understand the law behind such exhibitions.
Once someone sells a work of art, that owner of the art can still display it without the artist's permission, even for profit (this is closely related to the "first sale doctrine").
The first sale doctrine, codified at 17 U.S.C. § 109, provides that an
individual who knowingly purchases a copy of a copyrighted work from
the copyright holder receives the right to sell, display or otherwise
dispose of that particular copy, notwithstanding the interests of the
copyright owner. The right to distribute ends, however, once the owner
has sold that particular copy. See 17 U.S.C. § 109(a) & (c). Since the
first sale doctrine never protects a defendant who makes unauthorized
reproductions of a copyrighted work, the first sale doctrine cannot be
a successful defense in cases that allege infringing reproduction.
An exhibition is a display of originals with the permission of the current owners of those originals. Copyright pertains to making copies of protected work, not to the display or disposition of the originals.
The trickier point would be whether the owner of the original would acquire the right to photograph his own original work incident to ownership in the absence of an agreement to the contrary with the artist, for example, for use in an exhibition catalog or poster, perhaps on a theory of fair use, or perhaps on a theory of implied license.
I suspect that there is caselaw on this point, but haven't researched it.
While the first sale doctrine forbids an artist from holding onto display rights as a matter of public policy, it does not prohibit a sale of an original work from including a transfer of the copyright to that work or a license to make copies of that work, even if those rights could lawfully be withheld by the artist in a sale of the original work.
So, the question of whether there was an implied license to allow the owner of the original work to reproduce it for various particular purposes boils down to one of contract interpretation in the transaction by which the first sale of the original work from the artist to the first buyer of the work took place.
Also, the more likely it is that there was an implied license, even if it is not definitively established that there was one, the more likely it is that a court would find a reproduction to be fair use by the owner of the original.