Board Thread:Editing Discussions/@comment-6697950-20140730104841/@comment-6697950-20140730134744

Unofficial images is used specifically for images that are not official and can only be used for personal pages. Extra source is for all the official content that comes from various sources. Completely different purpose.

Either way, categories are supposed to make navigation easier. If there are many images that come from the same source (several pages worth of images), then I believe that sub categories should be created to make it easier to find image from the same source.