You can install a logo for each section on your site. This logo could be unique (fixed image) or animated to handle mouse hovering.
The installation of images for this section logo is exactly the same as the installation of an article’s logo.
P.S. The section logos have a recursive behaviour: in the event that a logo is missing for a given section, SPIP will try to substitute it with the logo of a parent section:
In the above hierarchy, and when there is a missing logo for section 221, SPIP will substitute in (an only for visits to the public site) the logo of section 22 or if that one is also missing its logo, SPIP will use the logo from section 2. Otherwise, SPIP will display the logo installed in the site root for the whole site.
You should note also that, if the webmaster has programmed it that way, a section logo could be used as a default substitution logo for any articles that this section contains.