This is a very interesting video with an interview with Richard Prince and the photographers whose work Prince has appropriated or stolen depending on your point of view. The particular imagery under discussion is work from the Marlboro cigarette campaign, showing the 'all American' cowboy. Though Prince has used other work and has turned his attention more recently to a softer target (non professional mostly) in Instagram.
The video is a fair and balanced overview of whether its is appropriation or just plain theft. To the photographers (and as a photographer myself) its theft. Specifically as it is straight copying, following cropping from the printed advert, with no re contextualising except within an art gallery world. It is however more complex and brings into discussion Copyright, fair use and the art market.
The three photographers (Norm Clasen, Sam Abell and Jim Brady) who created the original work are very highly respected and experienced, Sam Abell in particular having created personal imagery of great beauty and imagination from around the world.
So why does this matter ? Think if you made a piece of work and someone copied it and used it virtually straight elsewhere, without crediting you, irrespective of any money they might make from it. Would you be happy or annoyed ? Some might not care and say 'what the hell' but I think if you value your art and the effort you have put into the work, as well as your unique artistic vision then it should matter and be of concern.