A "banner image" refers to a large picture or graphic displayed at the top of a webpage, usually to grab attention or represent the theme of the website. Full definition
Finally, we have added a new banner image at the top of the client and fixed many bugs that were submitted to us. (goodereader.com)
The site has a much more modern design, featuring large banner images and it will expand or shrink based on the size of your screen or device. (ahparkfoundation.org)
I think you should use it as your head banner image in this blog. (kendieveryday.com)