Admins have the ability to display full resolution images on the backgrounds of text cells. This feature has only been used a handful of times and is not available to the general public. There is an unspoken rule, however, that any user can request FP to add a background image to their worlds. All you need to do is provide him with an image of your choosing, though FP can deny your request for any number of reasons.
Background images have been a suggested feature since the inception of modern OWOT in 2017, and were realized not too long after the site's launch.
List of worlds with background images
With all of the following worlds, there is an added option in the menu that lets you turn off background images.
Background images can exist at a singular location on a world, or cover the entire page in an infinitely looping pattern.
Located under the https://ourworldoftext.com/other/backgrounds/[image name] URL.
AndreiXYZ claimed /other in June of 2021 and is now technically the owner of all files stored under the namespace. Andrei placed the following list of background image files in /other, which has received minimal updates since 2021.
You can render a pre-existing background image on any world using the following script: