4. The method of classification of claim 3 , comprising a sequence of at least the following steps performed offline: extracting the visual features of a plurality N of images forming a learning base, during which the local features of each image are extracted and coded on the visual dictionary W v ; constructing the recoding matrix X; normalizing the recoding matrix X; performing an unsupervised classification step, referred to as a step of clustering the normalized recoding matrix, for generating the multimedia dictionary W m .
8. The classification method of claim 4 , wherein said step of clustering is performed based on a K-means algorithm.