Medical experts must perform legal medical assessments aimed at providing the scientific support required by the authorities before disputes raised, to know the approximate biological age of a living person. The Tanner staging, which describes the physical changes observed in genitals, chest and pubic hair, throughout puberty in both sexes, has been used as a methodology at the time of the forensic medical assessment of minor cases of age, involved in sexually explicit behavior, either in photos or videos suspected of child pornography. The virtual images, produce serious problems when defining the reality; leading to the commission of legal medical diagnostic errors. At present, there is no scientific evidence to support the forensic medical use of the Tanner staging, when evaluating photographs and / or videos on suspicion of child pornography.