The present invention relates to a method and a system for the local or remote authentication of an item, in particular a security document, with the help of a authenticating device, comprised in, connected to, or linked to mobile communication equipment. Said item carries a marking exhibiting a characteristic physical behavior in response to interrogating energy, such as electromagnetic radiation and/or electric or magnetic fields. Said marking may comprise physical and logical security elements, e.g. a barcode, or a characteristic particle or flake pattern, exhibiting a characteristic physical response.