arthistoricum.net, via which I have now come across a rich source of Goethe illustrations: the digital catalogue of the Frankfurt Goethe-Haus. The drawing, a "study for Werther, is by the German Impressionist painter Franz Skarbina.
digital museum site, I also found this contemporary "Idealportrait Werthers in Medaillon, darunter Szene mit Werthers Abschied von Albert und Lotte." It is by "D. Chodowiecki del.," and appeared in the first volume of Goethe's writings in the 1779 "Gesamtausgabe." The difference in sensibility between the two images is quite striking. Did Goethe's contemporary readers visualize Lotte as the finely dressed lady to whom Werther is bidding farewell? Everything Goethe writes about her in The Sorrows of Young Werther suggests domesticity, not finery.