Sculptures in public parks in US
It's OK to take photos. It's OK to sell the photos so long as the sculpture isn't the featured element of the photograph and you might be considered selling a reproduction or likeness of the artwork.
Even then, you would probably not be prosecuted.
Here is an example of an Eisenstadt street art image that has been created as a sculpture and is not travelling, and being photgraphed, all over the place.
I am among thoe who have photographed the statue. My understanding is thatTime Inc. owns the copyright to the Eisenstadt photo and has stated that Seward has violated their copyright, but has sofar declined to sue.
I also understand that although the sculpture is illegal it is nevertheless copyrighted and myself and the others who took photos of it have violated that copyright.
Please do correct me if my understanding is not correct.