Hello L-W, the poster is a picture of Carlos Gardel, and in the picture his cheerful expression could be interpreted as "winking", or he could actually be winking. The poster is up on the wall, probably at or above eye level. So in fact it is not the poster winking, that is the expression of the person in the poster. And he appears to be looking down at the viewer of the poster.
It should mean that in the poster, Carlos Gardel is winking. I haven't heard of winking used like this, but I have encountered other verbs used this way. It's not uncommon for people in photos and paintings to be talked about as though they are performing some action in real life: smiling, for example, or glaring or simpering.
"A poster of Carlos Gardel winks down from the wall." = There is a picture poster of Carlos Gardel on the wall; the picture shows Carlos Gardel winking; the picture is high up on the wall, so that the wink comes down to the observer.