marked automatically by who, and why is outsourcing the information to an 'automatic' third-party a "proof"? Why should that third-party be trusted?
The decision to trust the issuer or not is down to the entity viewing the information, and depends on the particular requirements of the situation. A zero-knowledge proof that I am over 25 issued by my local library may be enough for the local theatre to let me in to watch a suitably rated movie, but not for the local bar to let me purchase liquor (in the latter case a proof directly from a government entity would be more appropriate).