Not sure what you mean... do you mean you want to take a photocopy into the Bank and use it to open the account? The normal way would be to take the original in and the bank would photocopy it for tyheir records and give you the original back.
If you want a certified copy to send off in the post then it needs to be signed by someone official like a solicitor, Doctor or as I said, your Bank.
Spot on dzug. There is nothing special about solicitors and doctors (eg) that gives them 'authority' to authenticate documents rather then, say, a taxi driver (eg). I am sure the relatives of HArold Shipmans victims would agree.