Method for determining an operating parameter of a wind power plant comprising: - acquiring a sequence of images of the wind turbine , in particular during production operation of the wind turbine , wherein the images are acquired from below a nacelle of the wind turbine and an optical axis of the image acquisition is parallel or at an acute angle to a tower axis of the wind turbine , and - determining the operating parameter on the basis of the acquired images, characterized in that an initial first characteristic point is determined in one of the images , the initial first characteristic point being a pixel of the wind turbine whose image position does not change due to the rotation of rotor blades of the wind turbine between two of the images , - that edge detection is performed in the image , - that a curve is approximated by the detected edge and thus an approximated curve is determined, - that a second characteristic point is determined in the approximated curve , the second characteristic point being a point of the approximated curve which is closest to the initial first characteristic point , or in that the second characteristic point is a zero point of the approximated curve , - that the initial first characteristic point is shifted to the second characteristic point and - that in temporally successive images a further characteristic point is determined, and in that a spatial position of the further characteristic point is compared with the spatial position of the shifted initial first characteristic point , and that a spatial deviation of the further characteristic point from the shifted initial first characteristic point is determined, the spatial deviation representing the operating parameter, the operating parameter being the deflection of the tower and/or of the nacelle. - acquiring a sequence of images of the wind turbine , in particular during production operation of the wind turbine , wherein the images are acquired from below a nacelle of the wind turbine and an optical axis of the image acquisition is parallel or at an acute angle to a tower axis of the wind turbine , and - determining the operating parameter on the basis of the acquired images, characterized in that an initial first characteristic point is determined in one of the images , the initial first characteristic point being a pixel of the wind turbine whose image position does not change due to the rotation of rotor blades of the wind turbine between two of the images , - that edge detection is performed in the image , - that a curve is approximated by the detected edge and thus an approximated curve is determined, - that a second characteristic point is determined in the approximated curve , the second characteristic point being a point of the approximated curve which is closest to the initial first characteristic point , or in that the second characteristic point is a zero point of the approximated curve , - that the initial first characteristic point is shifted to the second characteristic point and - that in temporally successive images a further characteristic point is determined, and in that a spatial position of the further characteristic point is compared with the spatial position of the shifted initial first characteristic point , and that a spatial deviation of the further characteristic point from the shifted initial first characteristic point is determined, the spatial deviation representing the operating parameter, the operating parameter being the deflection of the tower and/or of the nacelle. <EOS>