I disagree. People seem to be confusing their right to photograph with rights to profit. Copyright is simply about protecting reproduction rights. Anyone has the right to photograph the dog. I would argue that they do not have the right to produce prints, or postcards for profit without the consent of the creator of the outfit (the dogs owner) and the 'art' in the medium it is being expressed. The dog in pilgrims outfit was not your idea. Not your creation. By stealing the image with your camera for commercial use you are violating Copyright of the artist/creator. Costumes are recognised as Copyright if the costume is an original creation, or has commercial value within the photograph. Clothing cannot be copyrighted if it does not carry a logo, or trademark, or unique design. But, a costume does have Copyright protection. I would also argue that the dog in costume is actually a 'fixed expression in a tangible medium' - the costume has a contextual relationship to a very permanent environment.