xbmc no longer expects both banners and posters to be named the same.
the correct format is:
Show:
poster.jpg
banner.jpg
fanart.jpg
clearart.jpg
logo.jpg
character.jpg
landscape.jpg
Season:
seasonXX-banner.jpg
seasonXX-poster.jpg
seasonXX-fanart.jpg
seasonXX-landscape.jpg
season-all-poster.jpg
Specials
season-specials-poster.jpg
season-specials-fanart.jpg
season-specials-banner.jpg
season-specials-landscape.jpg
http://wiki.xbmc.org/index.php?title=XBM...odo%29_FAQ
From the XBMC Frodo release wiki, section 1.8:
1.8 How should local images be named for Frodo?
See also: Thumbnails
Since Frodo now supports both posters and banners simultaneously, and for other supported images, the following naming conventions are available for local images (Only required if the user wants to specify what image to use. Otherwise XBMC will automatically download images from the video scraper). Whenever possible, old Eden style naming is supported for backwards compatibility.
For folders (e.g. tvshows, movies in folders, or just folders on the filesystem)
poster.(png/jpg)
banner.(png/jpg)
fanart.(png/jpg)
Note: Movies in folders can also use the options under files below.
Season images reside inside the tvshow folder
season[XX]-(poster/banner/fanart).(png/jpg)
season-all-(poster/banner/fanart).(png/jpg}
season-specials-(poster/banner/fanart).(png/jpg)
For files (episodes, movies not in folders, video files)
[movie file name]-(poster/banner/fanart).(png/jpg)
[episode file name]-thumb.(png/jpg)
[filename]-(poster/banner/fanart).(png/jpg)