Carlotta was a holographic character in Kathryn Janeway's holoprogram of Leonardo da Vinci's workshop.
She was from Florence and posed as a model for the maestro and his disciples.
When the Doctor had to hide in the holoprogram in order to avoid detection by the Srivani, he posed as a painter and attempted to portray Carlotta. (VOY: "Scientific Method")
Carlotta was played by background actress Nathalie Huot who received no credit for her appearance.