A good book jacket should reflect its contents but can be a piece of art in itself. In this way it is very similar to the music album cover in the way that some, such as the Beatles Sergeant Pepper, have become as famous as the album itself. http://wellmedicated.com/lists/45-beautifully-designed-book-covers/
The cover is probably of secondary importance to writers and recording artists. Their paramount concern is that of the content that the cover encases which is as it should be. However, put a pretty girl on the jacket of a book and it may sell more copies than a representation of an inanimate object in much the same way as a sexy female model draped across the bonnet of a motor vehicle is used to sell cars.
The choice of a book cover can be an agonising one for the author and publisher who has to pick something to convince prospective buyers that there is something worth reading inside. With its first published book Peatmore Press chose a deliberately badly hand drawn picture for its first publication, Cogrill’s Mill, in the hope that it conveyed the light hearted nature of the novel. However, there is a danger that it might show a lack of quality which would be off putting to a potential reader.
A high vantage photograph of Woking, used to represent the fictitious location of Wellstone where most of the action takes place, was used on the jacket for Victim of Compromise. The thinking was that local readers would recognise the town and thus be tempted to buy.
A collage to represent the story was used for Gifford’s Games with the added advantage that the inclusion of a partial photograph of an attractive woman in the design might also tempt prospects to buy.
Time will tell whether these strategies will pay off. However, in the event they do not the publisher still has the option of changing the cover because unlike the jacket only very minor changes, such as corrections to spelling and punctuation, can be made to the content.