Retinal scans require close contact of user and scanner, a perfect alignment of the eye with a scanner, and no movement of the eye. The examiner is required to keep the subject's eye within half an inch of the instrument. The subject must focus on a pinpoint of little green light (to properly align the eye) and avoid blinking. A low-intensity coherent light is then transmitted through the eye and the reflected image of the retinal capillary pattern is recorded by the computer. Facial recognition analyzes the characteristics of a person's face via images input through a digital video camera. It measures the overall facial structure, including distances between eyes, nose, mouth, and jaw edges. Retinal scanning is the most intrusive form of biometric. If facial recognition is the equivalent of pickpocketing your secrets, then a retinal scan equates to being mugged. If you see police photographers taking photographs of crowds (for instance, at a demonstration), you can safely assume that the faces in these photographs are being electronically analysed and catalogued.