There's no reason to doubt that Sebald's darkened (newspaper) reproduction is from a picture of Nabokov, taken in August 1971, near Gstadd, in a walk with Dmitri. The reproduction in p.122 in Jane Grayson's "Vladimir Nabokov"(Penguin) is a colored one, but I subtracted its colors to help in a comparison bt. Sebald's and Grayson's images.