I used to find that a square image was perfect. It showed up well when the person rang, because it left space above and below for the various buttons. It also suited the Contacts app and iCloud, because their image placeholders are square. With iOS7 the incoming all screen now needs to be 640x1136 (as seen in the promo pictures for an incoming call), but the app and iCloud placeholders are circular. Has anyone figured out the best position to have someone's face so it fits well in both situations?