Photokey is SeaWorld's version of Photopass, though the scope is on a MUCH more limited scale. These include ride photos, park entrance photos, special event pics (with Santa at Christmas, etc.), photos with the characters in Sesame Street, and tour photos.
When you arrive at the park, go to the kiosk to redeem your photokey entitlement. The machine will spit out a credit card-sized paper card that you will need to take to the Adventure Photo location just inside the park entrance. There, they will set up your account and give you a hard card (your Photokey card) for collecting your pictures. When you go to have a picture taken by a park photographer, show them your photokey card and they will take a picture of the bar code before capturing your photo. After you disembark from a ride, give your card to the photo station attendant and they will add your ride pic to your account. Download the app on your phone, and you can access all of your pictures taken during your annual pass period. You can also log in to your Photokey account online via a laptop or desktop computer and edit, add borders, etc.