Jenkins has a mechanism known as "User Content", where administrators can place files inside
and these files are served from http://yourhost/jenkins/userContent. This can be thought of as a mini HTTP server to serve
images, stylesheets, and other static resources that you can use from various description fields inside Jenkins.
Note that these files are not subject to any access controls beyond requiring Overall/Read access.
See Git userContent plugin for how to manage these files through a Git repository.