Yes, I have seen this Snapchat streak phenomenon with my little brother and his friends. They constantly send completely random pictures to each other, i.e. they open the camera app, take a picture of the ground, of the seat in front of them in the car, etc. and then immediately send it to a number of their Snapchat friends. When I had Snapchat installed for a short while he started sending me those pictures too, which in the end led to me blocking him. From what my brother said there is a lot of competition around who can keep their numbers the highest. Quite a strange thing to watch as an outsider.