(CNN) -- At an auction at a gallery in New York recently, a piece of artwork sold for a higher price than had been anticipated by the auctioneers: $4,080. 

It wasn't a very big piece of art -- just 8-by-10 inches. Technically, it wasn't even art. It was a glossy black-and-white photograph. It had a slight imperfection: there were staple holes in the upper left-hand corner. 

Someone had written all over the front of the photograph. The person who had scrawled on it was, in fact, the subject of the photograph. He had written: 

"To Patricia Keating, with very best wishes, John Kennedy" 

That is what made the photo so valuable to someone: Kennedy had held it in his hands, had run his pen over it. The owners of Swann Galleries, where the signed photo was auctioned, believe that Kennedy had autographed the picture in 1956, when he was a United States senator. The picture itself wasn't worth much; but his signature, personalized to Patricia Keating. ... 

"As far as we know, she wasn't anyone famous," Rebecca Weiss, a Swann Galleries employee, told me on the day after the auction. "There's no particular significance to her name." 

Then why would someone pay more than $4,000 for the photo? 

Weiss told me that the identities of the buyers and sellers at Swann auctions are kept confidential, so she could not disclose who had consigned the photo for sale, or who had purchased it. But she said there is a pretty safe rule of thumb about the sale of autographs of renowned men and women: 
What was his occupation then?
1956, when he was a United States senator.