Non-line-of-sight (NLOS) optical camera communications (OCC) is a potential wireless communication technology, which offers robustness to blocking and blooming effect, higher data throughput over longer transmission distances compared with line-of-sight OCC. In this work, we propose a wavelength division multiplexing (WDM)-multiple inputs multiple outputs (MIMO) NLOS OCC system with multi-level pulse width modulation (MPWM) and difference-based pulse width recognition (DBPWR) schemes. Signals on different color channels are separated through the RGB filter of the CMOS camera, while MPWM signals on the same color channel are separated using the DBPWR algorithm. Compared with the conventional threshold-based demodulation scheme, the proposed DBPWR scheme has lower complexity, higher reliability, and improved sampling frequency offset tolerance. A total data rate of 10.8 kb/s is experimentally demonstrated over more than 2 m NLOS link using the proposed WDM-MIMO OCC system, which is sufficient in many Internet of things applications.