Section 76. Copies of books, papers, documents and records in any department of the commonwealth or of any city or town, authenticated by the attestation of the officer who has charge of the same, shall be competent evidence in all cases equally with the originals thereof; provided, that, except in the case of books, papers, documents and records of the department of public utilities or the department of telecommunications and cable in matters relating to common carriers, and of the registry of motor vehicles, the genuineness of the signature of such officer shall be attested by the secretary of the commonwealth under its seal or by the clerk of such city or town, as the case may be.