Usually a subject will have no ownership rights over a photograph. As the author of the work you are the copyright owner unless you have made a contract with them that assigns copyright to them. However there are signficant limitations that apply to what you may do with the photograph despite ownership of copyright:

• Any photo that violates a subject's normal expectation of privacy may be an offence under human rights law and/or data protection law. 
• If commissioned to take a private portrait or other photo for personal purposes (eg weddings), you will be unable to publish without their permission.
• For certain types of usage you may require a model release. 
• There are other legal limits on what you may do with the photo, eg defamation, harassment etc.