After receiving your Rotom dex, you will eventually have access to the Poke Finder. It is a special part of the Pokedex that allows your to take snap of photos in the Pokemon world. It is like the instagram social media app in Pokemon where people rate how nice and good you took pictures of the different Pokemon. As more thumbs up you receive, additional features will be unlock in your Poke finder.
Having the Best Photos
The Pokemon Company International. (2016). Pokemon Sun & Pokemon Moon Official Alola Strategy Guide. London: Pokemon Company.