Generally, a photographer owns the rights to a photograph but your right to use the picture depends on several other facts such as where the picture was taken, is the person in picture famous and whether any release was obtained from the subject of the photograph. For example, if you were retained to take pictures at person or families home, you could be invading their right to reasonable expectation of privacy. Children's rights are also protected. Your publication of the picture without permission can leave open to legal action.
Copyright belongs to you absent a work for hire arrangement or copyright assignment, which you don't mention. Here's where you messed up. Professional photographers should have a written agreement that allows promotional use of photos they take, such as in a portfolio or advertisements or on a website to show the quality of work. Sounds like you did not do that. My advice is don't use these (for the reasons well stated by my colleague from NY) and see a copyright attorney to get a release written so you are covered and authorized to use future proofs or actuals the client did not want.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.