If your Masthead images are uploading normal but look blurred or distorted on the Storefront, you'll need to make sure the Image Dimensions are set to 1170 pixels wide by 760 pixels tall in Editorial / Asset - Application Settings. Even though you uploaded the Masthead Image via the Business listing in Marketplace / Businesses, the system still see's the Masthead Image as an Image Asset which is managed by the Editorial / Asset application.