A three-dimensional printing system for solidifying a photocurable resin in a layer-by-layer manner at a build plane includes a scan module, a transparent plate, a sensor, and a controller. The scan module is configured to scan the light beam along two axes to address the build plane. The transparent plate is positioned in the optical path between the scan module and the build plane. The transparent plate has at least one reflective feature in the optical path. The sensor is mounted above the glass plate and is positioned to receive light reflected from the reflective feature. The controller is configured to operate the scan module to scan the light beam across the build plane, receive a signal from the sensor when the light beam impinges upon the reflective feature, and analyze the signal to verify a proper alignment of the light beam to the build plane.