The Sticker Book is another way of cataloguing which Pokémon you have seen within the Augmented Reality Viewer. These Stickers have a variety of functions
The Sticker Book
In order to get stickers, you need to bring in a Pokémon in the Augmented Reality feature that you have already obtained in the Pokédex. When they appear from the AR marker, they will automatically be registered into your sticker book. However, there is another sticker you can get. If you take a picture of the Pokémon in Augmented Reality, you will also receive a special Photo Sticker.
While these stickers would seem to just catalogue the Pokémon which you have found, they do have an extra feature. More aspects of the game are unlocked as you pass certain numbers of stickers. There's enough space for one of each Unova Pokémon plus any alternate forms
The features unlocked are as follows