I meant the details of the picture, that I mentioned. Yes, the picture as such is important I guess. It identifies the genre of the book on the shelve, before you have read anything. Romance, idyllic landscapes and so on, that attracts buyers who look for this kind of reading.
Well, there are different ways to approach this, I guess. Some authors go without any pictures, letting the imagination of the people spark curiosity (if it works). Or they use a simple drawn symbol.