When taking photos, quite frequently, the eyes of people will be captured as being red, this being called the red-eye effect.
This happens when the camera flash is too close to the camera lens and the background lighting is not powerful enough.
This photo effect can be either prevented, by ensuring proper light when taking pictures, or by using a dedicated application.
Currently, there are numerous graphic editors capable of fixing this problem by desaturating the red color.
Red eye removal is a function usually integrated within many complex graphic editors, but one can also use other apps that focus solely on this task.