1. A method of detecting an anomaly on an internal surface of a tyre through digital processing of an image of the internal surface of the tyre, the method comprising steps of: capturing a grey-level original image (f) of the internal surface of the tyre and transforming the original grey-level image into an orthonormal space, in which an x-axis (OX) represents a circumferential direction, and in which a y-axis (OY) represents a radial direction; transforming the original grey-level image using a predetermined series of filters (F 1 f , F 2 f ,. .. F L f ), to obtain a multivariate original image; splitting the multivariate original image into multivariate sub-images (W F k ), to obtain predefined tiling in the axial direction and the circumferential direction; transforming each of the multivariate sub-images is transformed into one-dimensional vectors using a given descriptor (H, G,. .. N), to obtain a simplified multivariate image (K W F , G W F. .. , H W F ) formed from a collation of the vectors; reducing a number of dimensions of the simplified multivariate image data using a data analysis tool, to obtain a reduced factorial space; and, in the reduced factorial space, evaluating a distribution of sub-images containing an anomaly in relation to a distribution of sub-images containing no anomaly, in order to assess a separating power of the given descriptor.