Almost the only thing that can be said incontrovertibly about this painting of two nearly identical women sitting up in a bed and holding two virtually identical babies, is that it is unlike any other known painting.
A popular notion is that the two mothers are twins. Their elaborate, formal dresses, in the fashion of early 17th-century England, are very similar, for all their small, subtle differences.
The women's coiffures and postures, their fixed stares and unsmiling, closed lips - even the way in which they hold their swaddled babies - are alike. All of these matching characteristics have fed the idea of twins being the picture's subject.
But scholars refute the twinhood theory by noting that the eyes of the mothers and their babies are of different colors.
The most thorough investigation into this mysterious picture - the artist is also unknown - was published by archivist John T. Hopkins in 1991.
Mr. Hopkins describes it as "a startling genealogical artwork based on a combination of circumstances the exact nature of which may never be resolved."
Hopkins determined that records of birth and marriage that might have answered the questions about the sitters no longer exist. He calls the painting "The Cholmondeley Sisters," while Tate Britain, its owner today, calls it "The Cholmondeley Ladies."
Most of its existence has been spent in the ownership of the Cholmondeley (pronounced "chumly") family in Cheshire, England.
The painting was recorded in 1882 as "an antient [sic] painting of two ladies, said to be born and married on the same day, represented with children in their arms" in "the passage leading to the sleeping rooms" of one of the family's houses.
Hopkins guesses that the mothers may have shared the same birthday, though some years apart, and that "they may have been married in the same chapel." He further speculates that they may have given birth to either their first or second children "on the same date."
A local (provincial) artist in Chester may have been commissioned by the ladies' mother "as a commemorative portrait of the two births."
So overall, there remain many "maybes."
Nevertheless, the arresting nature of the image overrides its inconclusive history. It speaks directly - and a little naively - to the imagination. Whatever its original purpose, it appeals to our modern fascination for the enigma of identity, for what makes people alike yet dissimilar.