It is my understanding that in collage works and the like, the artist has copyright over their creative inputs to the resulting piece, but does not gain any rig

It is my understanding that in collage works and the like, the artist has copyright over their creative inputs to the resulting piece, but does not gain any rights over the bits they cobbled the final together from. If I understand it correctly, even if the museum created a fancy collage for the side of the building, yes they would own that arrangement, but not any of the paintings which went into it. They still couldn't stop you from sharing images of the original works therein.