Half a dozen years ago, our current president published a book about his son’s death from glioblastoma. Titled Promise Me, Dad: A Year of Hope, Hardship, and Purpose, started with Beau Biden’s plea to his father not to let grief overcome him. (The loss of the Delaware senator’s wife and daughter in a car accident in 1972 almost derailed Biden’s life, including his political career.)

I found an autographed copy of the book, simply inscribed “Joe Biden,’’ in Savers in Boston’s West Roxbury for $4.49. The forgotten best seller did, nevertheless, offer a treasure, the mystery photo above.

There are almost no clues as to the identity of this young girl and, presumably, her  younger brother. It’s printed on Kodak Xtralife II paper, but who uses prints in this age of computers and online libraries? The buildings look recent – faux Georgian – although the cobblestone street could be European.

Looking at the lass’s auburn hair and complexion, we could guess that these children are Irish.

There’s a story here, at least in our imaginations. But, promise me, Dad, that you will date your photos and tell us why images like this represent a memory worth keeping.

An architectural and photo historian, William Morgan is a frequent contributor to New England Diary. His latest book, Academia: Collegiate Gothic Architecture in the United States, will be published in October.