This may help -
https://www.phpbb.com/community/viewtop ... 4&t=574022
2) If you want a banner like ours, then get the image the same size as your banner area which should be around 850px x 129px or whatever. Place the image inside you styles images folder. The "images" folder that is inside the "theme" folder. Upload the image to your web server ready for use.
Change the background-image property to your new image which can be a jpg if you wish. So it would look something like this: