In general, the photographer owns the copyright to a photo they take, unless they’ve transferred those rights in writing or created the image under terms that assign copyright elsewhere.

But copyright ownership is separate from whether you’re allowed to publish or sell the image. That depends on local law and on what’s in the photo. Limits can apply to:

• recognizable people and privacy/publicity rights
• copyrighted works shown in the image, such as artwork
• buildings, statues, and other works in public spaces, which may be covered differently by local “freedom of panorama” rules

So the usual answer is: you normally own the photo, but you may still need permission or consent for some uses, especially commercial ones, depending on your location and subject matter.

Example from the community answers: in Germany, publishing a photo with several people may be allowed without permission if no one person is singled out, but laws vary by country. If you need certainty for commercial publication, check the law where the photo was taken and where it will be used.