  In this paper, we propose a model protection method by using block-wise pixel
shuffling with a secret key as a preprocessing technique to input images for
the first time. The protected model is built by training with such preprocessed
images. Experiment results show that the performance of the protected model is
close to that of non-protected models when the key is correct, while the
accuracy is severely dropped when an incorrect key is given, and the proposed
model protection is robust against not only brute-force attacks but also
fine-tuning attacks, while maintaining almost the same performance accuracy as
that of using a non-protected model.
