Figure 6: (a) Example of one of the set of images included in the preservation copy of a compact cassette. Each element should be clearly visible in all its details, so usually a preservation copy contains from four to eight images. It is recommended that at least one includes the carrier with all its accompanying material—especially if these are not listed somewhere else in the textual documentation. Below the document's signature, a small ruler can be observed: according to the recommendation of the Italian Ministry of Cultural Heritage [53], this simple object conveys the real proportions of the depicted elements. (b) Serious corruption of an optical disc: this image should be stored in the discs' preservation copy in order to add information about the artifacts of the audio signal.