By default photographers own the full copyrights to photos they take. As the copyright holder, they can authorize or restrict usage of the photos in any manner they please.
Since they own all rights to their photos, photographers can sell the copyright to those photos outright if they'd like, but that would mean they'd be releasing all rights to it themselves, this also means their work could be used inappropriately, so this is done rarely. A more common way is a photographer will have the client sign a high resolution release form that will give them the rights to use the photos under the agreed terms between themselves and the client.
There are a wide variety of ways photographers license photos, including payment for each use; licenses to specific magazines for one article; product licensing where royalties are paid as products are sold; commercial use for advertisements. The type of license agreement designates how the photos can and cannot be used, but the copyrights to those photos remain with the photographer.
Since they own all rights to their photos, photographers can sell the copyright to those photos outright if they'd like, but that would mean they'd be releasing all rights to it themselves, this also means their work could be used inappropriately, so this is done rarely. A more common way is a photographer will have the client sign a high resolution release form that will give them the rights to use the photos under the agreed terms between themselves and the client.
There are a wide variety of ways photographers license photos, including payment for each use; licenses to specific magazines for one article; product licensing where royalties are paid as products are sold; commercial use for advertisements. The type of license agreement designates how the photos can and cannot be used, but the copyrights to those photos remain with the photographer.