Work for hire is a different concept from who pays. If you get a portrait photo made, you pay the photographer, but that doesn't make it a work for hire. The copyright in the photo will belong to the photographer, unless the photographer was employed by a portrait photography company, in which case it would be a work for hire, and the copyright would belong to the company. There are obvious caveats to that, eg there might be an agreement between the photographer (or company) transferring copyright to the subject. There are also weird cases, eg in academia. It seems clear to me that academic staff are employed by their universities to teach and do research, and therefore the copyright in what they write to those ends should belong to the university. When I raised this at one university, I was told, this hasn't been a problem, forget about it!