Must it be as late as the Middle Ages at all? Here is one from a Greek pottery piece:
http://en.wikipedia.org/wiki/Hand_spinning#mediaviewer/File:Woman_spinning_BM_VaseD13.jpg
The caption (yes, I found it on Wikipedia; that's Google image search for you) reads:
"Woman spinning. Detail from an Ancient Greek Attic white-ground oinochoe, ca. 490 BC, from Locri, Italy. British Museum, London."
Cathy, thanks for the links! That is one of the quite early ones that originate in (Middle) Europe, as far as I've progressed in my search.
And yes, they have to be medieval, and preferably from Europe/Middle Europe. There's no problem at all in finding Greek spinners doing their thing - but the technique shown is different from the high/late medieval pictures.