Hello !!!

So i have an island which is a QGraphicsPixmapItem and it looks like this :

island.jpg

And what i'm trying to do is putting rocks all around the island, but i don't know how to do that ( i know how to put them on the scene i just don't know how to position them around the island )... so i was wondering if there is any kind of a way in which i could do this or do i have to figure out an algorithm on how to go all around the island ?