I don't remember the first time I heard this expression, but I think it's great. If you're not familiar with it, Ingres was a 19th century French artist, famous for paintings such as this:
The "Violon d'Ingres" is also a very famous photo by the great Man Ray:
which suggests that for the photographer, women were his "violon d'Ingres".
Go on, I dare you! Try and fit this expression into your conversation tomorrow.
And my "violon d'Ingres"? Hmmm. Maybe reading, maybe arts and crafts. I'm not sure... What's yours?