Abstract: Disclosed is a method of visually inspecting a wind turbine generator (WTG) and parts thereof during operation. The method comprising acts of pointing a visual inspection system with a field of view about a line of sight in a plane of rotor blade of the wind turbine generator (WTG); of capturing multiple images of the field of view using the visual inspection system; of selecting at least one reference image amongst the captured images or from elsewhere; of comparing the at least one other captured image with the at least one reference image; and thus inspecting structural aspects of the wind turbine generator (WTG) as a function of the result of the act of comparing.