It began with Godot13 nominating a scan of a banknote at featured images. That is not unusual. Getting acess to the US National Numismatic Collection with a medium format camera and an aparently impressive knowlegde of how to use it will give you a pretty large number of feature picture candidates (enough to break the wikicup certianly). Godot13’s currency images thus usualy pass through with little fuss.
The problem in this case is that the banknote the image is of (An 1880 Liberian 25-cent note) was previously thought not to exist. This results in one of those rare cases where an image breaks wikipedia’s no orginal research policy. Images are largely exempt unless they “illustrate or introduce unpublished ideas or arguments” in this case the idea is that the note exists. Sure it almost certianly does (although fake items have got into museum and archive collections before) but that is still originaly research. Happily the numismatics mob are second only to the railway anoraks in generating reliable sources for everything so this issue should resolve itself soon.