The invention relates to a method and to a device for authenticating and/or identifying persons, objects, or service systems. In said method, a material, a construction, a substance, or a composition, or an image thereof, either changes itself or is actively changed, by means of a physical, chemical, or mechanical influence or feature, such that the resulting structure or feature is unforeseeable. If an image of said material, of the construction, of the substance, or the composition recorded at a later time is compared with the image stored in a storage means, the person and/or the object and/or the medium and/or service system is positively authenticated if the material, the construction, the substance, or the composition has at least partially changed between the two times in comparison with the image stored in the storage means.