Currently, Snapchat users can doodle, animate and add static stickers to photos and videos. However this future update for iOS will track objects, like people and animals, and allow users to add stickers to those objects, which will scale and move with it in real time.
For example, the usr can put a 'top hat' sticker on a kitten, as the kitten walks around, the hat sticker will move with it.
While the feature is now available on Android, iOS users might need to wait a few days before the update goes through Apple's review process. Either way the free update should be welcomed by all the creativity that surrounds the social network.