1. A method of optically assessing a portion of a wind power installation, the method comprising: placing a camera at a distance in front of the rotor of the wind power installation; successively orienting a camera toward surface regions of the rotor blade to be assessed; using the camera, recording photographs of the surface regions to be assessed; using a position detection device, determining the positions of the photographed surface regions, wherein determining the positions of the photographed surface regions comprises: detecting at least one dimension in a longitudinal direction of the surface regions to be assessed from a first reference point to a second reference point of the surface regions, recording at least one first reference angle that specifies a first orientation angle relative to the first reference point, recording at least one second reference angle that specifies a second orientation angle relative to the second reference point, recording a current orientation angle that specifies an orientation angle relative to the surface regions to be assessed, and determining a current position of the surface regions to be assessed in relation to the longitudinal direction of the surface regions, the current orientation angle, and the reference angles; associating the determined positions with the recorded photographs; using the recorded photographs to identify a crack in the rotor blade at the determined positions; and correlating the crack with a location on the rotor blade.