The Templateer gives you the ability to enable the WordPress custom header image function. This is the only feature that requires you to edit your themes header.php file. It is enabled through the new Advanced Options screen.
The only info you need to provide is the height and width of your header image and to make a small edit to your header.php file. The WordPress custom header function not only allows you to have a custom header image but to also have a different header image for each page or post using the Featured Image function.