Book covers are different in different countries, even when the same books are inside them. Tom Lamont compares notes in yesterday's Observer, taking particular exception to translations into foreign languages. And it works the other way around too.
Compare and contrast, for example, Sasa Stanisic's book in German (vaguely nostalgic but rather odd photo) and English (picture of gramophone for the very dumb), Julia Franck's in German (puzzling shadows) and English (something out of Brief Encounter) and Alina Bronsky's in German (red on red just so you realise it's about Russians) and English (purple and hip). And I'm not even going to mention the British cover of Wetlands.
Günter Grass' Tin Drum, on the other hand, just gets a bit of a grooviness injection in English compared to German.
I think we can safely say, based on this extremely wide survey, that English covers dumb German books down visually so people aren't scared of them being foreign and difficult. Which is a perfectly legitimate strategy.