A contact image sensor, or CIS, is a specialized type of line scan sensor used in check scanners. While line-scan sensors in general are used to capture images of moving objects in single-pixel “slices,” contact image sensors are specifically designed to do that job from a fixed distance very close to (or nearly in contact with) the object being photographed.
For scanners in particular, contact image sensors save a lot of space; if the image apparatus was a proper “camera” that used lenses and adjustable focus distances, it would be much more bulky and increase the size of the device. The form factor of a CIS allows it to be flat up against the feed path, and takes up much less space overall.
