Red eye often happens due to the use of flash in low light conditions as the light hits the eye very quickly and into the retina. It then bounces off of the back of the eye and emits a red color due to the blood vessels there. Although more professional modern cameras and flashes generally prevent this from happening, red eye may still occur with simpler, smaller cameras (including smartphones). There are various software solutions for red eye removal available on mobile devices and desktops, some of which require manual processing to get good results.
Social networking sites allow users to upload images or other types of files that are immediately available to other users via news feeds or notifications. In some cases, attackers can directly spread infected files, but more commonly, they leverage the viral effect and the fact that users are simply unaware that their files are infected through sharing and collaborating with others. As a site owner or application developer, it is your responsibility to protect users and prevent these situations from occurring. Fortunately, Cloudinary makes this easier with its Metascan add-on.