I think the photograph idea gives a hint (though is unlikely to be unique), say there was a picture of the Queen/President in some recognisable location in thei

I think the photograph idea gives a hint (though is unlikely to be unique), say there was a picture of the Queen/President in some recognisable location in their office. They could be asked, "where is the xxx standing in the portrait in your office". This may be what the linked article says, don't know, haven't read that (yet). EDIT on thinking about it, a password is an answer to a question (what is the shared secret?), it's not the password they don't know, it's the question.