The purpose of 15-puzzle (also called Gem Puzzle, Boss Puzzle, Game of Fifteen or many others) is to arrange numbers from 1 to 15 (or a picture cut in 16 pieces) simply to making them slide.
It consists of 15 smalls tiles that slides in a frame of 16.
Click one of the tiles next to the empty tile to slide it into the empty space.
Rearrange the tiles until they go from 1 throught 15 in left to right order, or the image is in right order.
The program mixes the image by randomly moving the tiles. So the solution already exists.
The game proposes several photos (cut in 16 or 9 tiles) to be reconstitued, and the possibility to choose a photo which is on your telephone or tablet.