So I'm displaying a bunch of book covers from our library catalog (new additions), and I'd like an icon (well really two), that suggests changing the cover size. My other thought would be to have the small book on top of the bigger one. Or maybe some diagonal lines from the corners of the small to big book. Any suggestions for what might make a good icon to show this? My initial foray (below) doesn't really do the job, at least not from the small sample of user testing I've done.
Increase cover size: