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

Image Name Method
Note - Makes Pokémon use their cry Earn 30 Stickers
Ability to use old pictures as a background Earn 50 Stickers
Can now display 9 Pokémon at once Earn 70 Stickers
Can use the slider in the Scale Settings menu allowing you to show Pokémon to scale and manipulate size. Earn 100 Stickers
Can use the Stopwatch feature Earn 150 Stickers
Can now display 10 Pokémon at once Earn 200 Stickers
Can now display 11 Pokémon at once Earn 250 Stickers
Can now display 12 Pokémon at once Earn 328 Stickers