the invention relates to a document bearing an image or a text , broken down into a large number of elementary areas with which are associated respectively a large number of indexes . according to the invention , each index includes a group of dots placed on the document in the vicinity of the associated elementary area and forming a specific code for the said area , the indexes as a whole forming a location frame covering the said image or the said text and superimposed thereupon , each group of dots being readable by optical reading means cooperating with a data processing system comprising a data medium addressable by means of the said indexes .