Setting custom header images in The Mission and Bistro Theme is a unique feature of the new Croma framework.
One Question That we get quite regularly, Is how to set Header images where there is a unique and same header image for different pages. One example is where you want the team page and each of the individual pages for your team members to share the same header image.
The Coding behind the Header images involves an entry in the database to associate the Image with the specific post. That entry is created when you first upload the image into the post and click to mark the image as a banner post.
To create the same connection for images you will need to upload the image multiple times into every page that you want the image so that the connection and association in the database can be made for the image with each post or page.