We developed an optical module for distinguishing true and fake cracks in LCD and OLED glass board conveyer. We used a pulse modulated infrared laser to improve the functionality of distinguishing true and fake cracks formed at the edges of glass board. The conventional optical detection algorism sensing real cracks modified to reduce any misinformation of fake crack for true crack. We discussed the optimum operational conditions as functions of pulse modulation frequency and wavelength of the laser, transport speed of glass board, spot size and working distance of a focused laser beam.