Waves (acoustic, optics, radiofrequencies) can naturally encode informations over their various degrees of freedom, and their propagation in various environment may be seen as a processing step on this information. In the optical domain, photonics is an ideal technology for low-energy and ultrafast information processing, and photonic computing is currently seeing a surge of interest, with exciting perspectives. In Machine Learning, optics is naturally well suited to implement a layer of neural networks, via either in integrated or free-space approaches. However, most proof-of-concepts of optical machine learning to date are limited to modest dimensions, single or relatively shallow artificial neural layer networks, and to relatively simple ML tasks.