According to an article in The Washington Post newspaper, "La Divine Comtesse was born in Florence on March 22, 1837, as Virginia Oldoini, the daughter of a noble Florentine diplomat in what was then the Kingdom of Sardinia and Piedmont. Adored from childhood for her beauty, intelligence and capricious personality, she was married at 16 to Francesco Verasis, Count di Castiglione, a rich widower 10 years her senior. Their only child, Giorgio, was born a year later." This permits dating images of her wearing this dress. He would have been born around 1857 and looks to be maybe five, so the date for this photo falls in between 1860 and 1865. This picture was part of a 1930 album consisting of 18 photos and 3 gouaches between 1863 and 1867 inspired by her, allowing the date to be set at around 1863.
Upgrade image posted 19 January 2017 from mashable.com/2016/05/03/virginia-oldoini/?utm_cid=mash-com-fb-retronaut-link#FAcs9.komkq0; monocolor tint removed. Also posted to the Countess of Castiglione’s Subalbum here.