The simplest way to ensure that the rights information of the ‘physical’ object and the digital object coincide so is by not claiming additional rights that may result from the digitisation of content. This is something that we particularly encourage you to do in works that are in the public domain, as described in our Public Domain Charter.
In any case, rights on the reproduction of a public domain work can only be legally claimed in a few circumstances, as described in this post.
If you still differentiate between two layers, for instance because a photographer digitised sculptures in a way that makes their photographs original, here is what you should consider to choose a rights statement that accurately reflects both the content and the digital object:
If the content is protected by copyright, but the digital reproduction is not, the rights statement should communicate the in copyright status (through a Creative Commons License, or an In Copyright Rights Statement).
If the content is not protected by copyright, but the digital reproduction is (and you wish to claim the rights), the rights statement should communicate the in copyright status (through a Creative Commons License, or an In Copyright Rights Statement).
If neither the content nor the digital reproduction are protected by copyright, the rights statement should communicate the out of copyright status (through the Public Domain Mark or an Out of Copyright Rights Statement).