For static in-page banners you can deliver images that match the size of the banner. In this case, it is also recommended to deliver a larger (higher resolution) images, with the same aspect ratio of course, for sharper display on high pixel density screens (like retina screens).
In the case of Rich Media formats, fees may apply. Please contact our sales teams at email@example.com.
Rich Media formats should be built on our HTML templates and delivered through our previewer. More information available in the following article: Use our Templates and Previewer.