ca. 1580 Bianca Cappello, Second Wife of Francesco I de' Medici by Alessandro Allori (Galleria degli Uffizi - Firenze Italy)
Bianca Cappello de Medici wears a characteristically Italian ruff-collar in this Allori portrait. The Wikipedia article for Alessandro Allori is here.
Upgrade image posted on 23 January 2013 from Wikimedia; spots throughout image removed with Photoshop by gogm.