The first time I visited the Leopold Museum in Vienna, I walked right into the portrait above left. I believe it was at the top of the stairs: Girl in a red dress, by the Austrian artist Ferdinand Andri (1871-1956)
It is an amazing picture that seems to consist of only two colors. The girl, who perhaps isn't a classic beauty, looks at you calmly, patiently.
When we visited Vienna again earlier this year, I was looking forward to seeing her again, but the picture was gone! It was in store, and I couldn't even find a picture of it in the museum shop.
The kind lady at the till rummaged through the whole storeroom for me and came up with a box of postcards of it, of which I bought a dozen or so.