1. An apparatus comprising: (a) a set of optical fibers; (b) a first light source; (c) a second light source; (d) a first camera; (e) a second camera; and (f) a computer; wherein (i) the first light source is configured to emit visible light that illuminates a scene, reflects from the scene, and is transmitted through the fibers from front ends to back ends of the fibers, (ii) the first camera is configured to capture a digital image of the back ends of the fibers while the visible light is being transmitted through the fibers, (iii) the second light source is configured to emit a set of pulses of infrared light that illuminate the scene, reflect from the scene, and are transmitted through the fibers from the front ends to the back ends of the fibers, (iv) the second camera is configured to take measurements, wherein each measurement measures, for a respective pulse in the set of pulses and for a respective fiber in the set of fibers, a time or times at which light from the respective pulse reaches the sensor after traveling through the respective fiber from the front to the back of the respective fiber; and (v) the computer is programmed (A) to calculate, based on the measurements, a map that maps, for each respective fiber in the set of fibers, position of a front end of the respective fiber to position of a back end of the respective fiber, and (B) to modify, based on the map, the digital image.