I believe you can judge a book by its cover, and my own aesthetic judgements, whilst subconscious; over time I realised that I was making a conscious assessment on the content, based on the cover. In many ways the choice of image was not arbitrary, at least to me.
Whether illustrations, photographic images or significant works of art they all contained an intertextual relevance to the texts that left an indelible memory for me. Steppenwolf by Hermann Hesse for example will be forever linked to Portrait of a Yellow Man by Paul Klee.