The photographer owns the copyright, however some places (Like Portrait Place) will sell the copyright to you.
I'm starting out in the photography business and for people I know, I currently let them use the photos as they wish, but make it clear that they are not to take credit for having taken the photo, and that I own the copyright which means that I can use a photo of them for any promotional purposes without their permission.

If I discovered someone using one of my photos and taking credit for having taken the photo then they are breaking the law.