Images that are used without the permission of those who request it will not be accepted.
This sentence is for the authors of banners to read. They may use images that are made by other people (all of them did) and they would need to get permission from the people who created the images before they include it within their banner. You're currently reading it from another perspective.
People who make images and want credit usually say so in various art boards. Those who do not request it give it out as open domain.
#1 is the creator taken from official RO art
#2 (Valkyrie Profile, not Randgris) and #3 (Fate Stay / YS) are images from Video Game art that is free to use.
#4 uses the Alberta and the Knight from the RO fanart kit.
#5 I've seen before and pretty sure it's by Gravity.
It's things like these that are fully drawn by individuals that require credits:
http://www.animepaper.net/gallery/scans/Naruto/item137580/http://www.animepaper.net/gallery/scans/Naruto/item133725/http://www.animepaper.net/gallery/scans/Naruto/item132120/Just don't ask why I used Naruto
Are we even technically qualified to use the fansite kit? We're promoting private servers.
It's all open domain. Even so, private server sites have nothing to do with the private server itself if you're going over moralities. This site also has nothing illegal on it.