Be able to select a thumbnail image in properties

Most of my books dont seem to show a thumbnail, just the generic (brown) book image with the title written over it. Would be nice if in properties I could add/select a thumbnail of the book in this case and save. Also I found many of the book titles are bigger than the generic image title box so they align wrong. Could do with increasing the size of the title box, or using a calculation to adjust the font size.