A scanner includes a reference backing member, a scan assembly and a light-obstruction member. The scan assembly, disposed opposite the reference backing member, scans a reference block of the reference backing member and an original block of an original in a scan region. The scan assembly includes a light source for emitting a first light beam in a direction toward the reference block, and emitting a second light beam in a direction toward the original block. The light-obstruction member, disposed between the reference backing member and the scan assembly, includes a light-obstruction part, disposed in a first optical path of the first light beam and outside a second optical path of the second light beam, for blocking a portion of the first light beam from reaching the reference block.