  Solving jigsaw puzzles requires to grasp the visual features of a sequence of
patches and to explore efficiently a solution space that grows exponentially
with the sequence length. Therefore, visual deep reinforcement learning (DRL)
should answer this problem more efficiently than optimization solvers coupled
with neural networks. Based on this assumption, we introduce Alphazzle, a
reassembly algorithm based on single-player Monte Carlo Tree Search (MCTS). A
major difference with DRL algorithms lies in the unavailability of game reward
for MCTS, and we show how to estimate it from the visual input with neural
networks. This constraint is induced by the puzzle-solving task and
dramatically adds to the task complexity (and interest!). We perform an in-deep
ablation study that shows the importance of MCTS and the neural networks
working together. We achieve excellent results and get exciting insights into
the combination of DRL and visual feature learning.

Computer Vision and Pattern Recognition