Storybird

Storybird allows the user to choose from a set of pictures drawn by a professional artist in order to create thir own stories. It somehow reverses the process of visual storytelling, i.e. from words to pictures, and requests the creator of a new story to start with the image and "unlock" the story inside.

This video explains the process

A couple of examples of books created by Storybird users:

Two Ways on Storybird
Colors Of The Rainbow on Storybird