The Branded Header (above) is the same component as the header image used globally at the top of the website. This is responsive, and must have two images created for it. One for Desktop and one for Mobile.

Both images created at 96ppi
Width Desktop: 3000px
Width Mobile: 1025
Height: There is no limit set on height constraints for either the Desktop or Mobile versions of this image.

PSD template with safe area markers for Desktop and Mobile found on Sharepoint here.