1. A method for processing an image of a surface of a tyre to be inspected, in which a three-dimensional digital image of the surface is acquired, in which each pixel of the acquired image is assigned a grey-level value proportional to an elevation of a corresponding point with respect to the surface, and in which pixels of the acquired image are placed in rows and columns, the method comprising: digitally processing the image by using a computer processor to: search the acquired image for zones of the surface, each of the zones including non-measurement points corresponding to pixels whose grey-level value is lower than a given threshold, the non-measurement points of each of the zones being erroneous points resulting from a shadow present when the image was being acquired; determine boundaries of an encompassing box that includes one or more of the zones; and, correct the non-measurement points of the one or more of the zones inside the encompassing box by, for a given row (li) secant to a zone of the one or more of the zones, correcting the non-measurement points of the zone by assigning to each pixel of the zone a grey-level value equal to a mean grey-level value of a set (Kij, si) of pixels of a reference segment (si) belonging to the given row (li) and positioned in proximity to the zone, wherein a result of the processing of the image is used to determine whether the tyre is in compliance with a reference.