This work proposes an ITO/HfO_x/TiN ReRAM crossbar device as a physical optronic reservoir (OR) for high-accuracy and simplified in-sensor computing. On static image classification, the OR can achieve 85% accuracy on the fashion-MNIST dataset, with just one trained readout layer. It also shows excellent robustness to device noise and variability—a significant standard deviation of 0.5 over normalized response yielded only 9% accuracy loss.