We’ve found that a landscape image for the left image space and a square image for the right space work best. The dimensions for the cover images (optimized for a 15-inch Macbook screen) are 1396x580 for the left cover image and 1066x580 for the right.
At this time, vendors cannot adjust or crop photos once they’re uploaded to your listing. So sorry about any inconvenience - we are working on the capability for cover images to be adjusted and cropped to best fit the top of your profile page.