If you are the creator of a 'work' then in most countries, you own the copyright unless there's a contractual agreement stating otherwise. Whether you can do whatever you please with the photos is a different kettle of fish. It's unlikely anyone is going to hire you to take photos and give you the right to do anything with them beyond hand over the prints to them. Also the contents of the photo may contain trademarks, other copyrightable works or may require model release etc. So as always the devil is in the detail.
Could you provide more detail? Who are you taking photos for, what are the photos of, and is there any contractual agreement in place?