If I asked you what was in this detail of Caravaggio's Bacchus (1597), and you answered "A carafe of wine," you would only be given partial-credit for your answer. Sorry. This detail, my friends, has been found to contain an early self-portrait of Caravaggio at his easel, shown as a reflection in the glass carafe.
You're aren't seeing it, you say? To tell you the truth, me neither. In actuality, you can't see this detail with the naked eye. It used to be visible, however, since it was mentioned by an Italian restorer in 1922. However, poor restoration efforts and the gradual darkening of this image have obscured this small portrait over time. Only recently did the portrait "resurface" through reflectography, and the image results were revealed last Friday at a conference in Florence.
You can kinda-sorta see the portrait of Caravaggio in this Telegraph article, which posted the reflectography results and circled where the portrait is located. I'm still not seeing too much, but I'm trusting that one can actually see a young Caravaggio, paintbrush in hand, with his arm extended toward a canvas on an easel.
Pretty cool, huh? I wonder if restorative efforts can make this self-portrait visible again to the naked eye.