Most photo assignments are done with specific licensing guidelines included. For example, if you hire Shadow to produce images for your modeling portfolio, you are of course permitted to use them for personal use, and the agreement will include a license for reproduction and distribution within your profession (eg. to agents, prospective employers, et al). However, you could not put that photo into a video or film or incorporate it into any derivative work (such as a movie poster) without prior written permission of the copyright owner.
Commercial use and other licensing is usually discussed up front and the appropriate license included within the fee charged. You must have a written license prior to any intended use outside personal use. Copyright buy-outs are rare but can be arranged. Otherwise, the photographer owns the copyright to the images created, by operation of law.