A contact image sensor module for scanning a document includes a light source, a photosensing array and a lens assembly. The light source emits a light beam to the document, thereby generating an optical signal. The photosensing array is used for converting the optical signal into an electronic signal. The lens assembly is used for focusing the optical signal reflected from the document and imaging the optical signal onto the photosensing array. The photosensing array includes a first photosensing element with a first width and a second photosensing element with a second width. The first width is greater than the second width.