AH, I get what you're saying. With the new 'drivers' for these, I guess that got a bit confusing.
No that isn't in a driver, it's loaded and edited via the media Tab in composer. For movie posters I think the recommended size is something like 2000x3000 or near, but that's far overdone for channels obviously.
I'd say 600x600 for those is plenty (they are square, unlike movies). You just load those direct into the system, or if you want, do one system and then export the media list to have handy to import whenever you want into other projects - THOSE get scaled by the system automatically.