Photo Disc

A Photo Disc is a round disc at the center of a PokéStop. They can also be found at Gyms by selecting the Photo Disc button. When a Trainer swipes the disc, a number of items will be given to the Trainer and added to their Items Bag.

Background
Visit PokéStops and Gyms around the world to gather Poké Balls, Potions, Eggs, and other items. Once a Trainer has collected items from the PokéStop, it will cool down for a short period of time. It will turn purple to indicate that it is inactive. Once the cooldown period expires, it will return to blue and to allow Items to be collected once again.

To help Trainers explore new places in the real world, PokéStops they haven't previously visited will appear surrounded by rings. Once they spin the Photo Disc, the rings will disappear indicating that they've explored the location.

Trivia

 * Trainers will earn bonus items when visiting Gyms controlled by their team. If they have a Badge for the Gym they're visiting, they will earn additional bonus items as well.