Schematic of the quantum secure imaging system. Polarized single-photon from Alice passes through the beam expanding lens, is modulated into specific spatial intensity distribution by the DMD, then transmits through the object, finally is coupled into Bob and detected by SPDs. The image of the object is reconstructed and the QBER is monitored to estimate whether the imaging process is safe and real. The angle of reflection from the DMD is exaggerated in the figure for clarity but is about 24° in reality.