I originaloly posted thisquestion on my wall and realized that I may have offficially only asked myself this, so I come to you "oh Master of the Wiki."
A while back you may have noticed that I uploaded the pic of Holo doing a shadow puppet on the wall beside her of a wolf.. With it I also gave the site I found it on, but I am not sure about the legality of it. It's a wallpaper site and there are no warnings about private property. Furthermore, I actually found the image in several places but here is one: http://hdwallpapers.lt/spice_and_wolf-hd-wallpapers/
There are many others there too not found on within this Wiki. Should we gather them?
Also Pininterest abounds with images of Holo and Lawrence (and other cast members) as well--in fact I found two sketches in "chibi" format which depict Holo and Lawrence with their family (litter).. Some are very good but I do fear the possiblity of cluttering up the Wiki.
Regarding legality of image uploads: You will really never have to worry about this. If its on the internet available to all it's basically "fair-game". I am an admin on a wiki that got 3.9 million views last week and we have never ran into that problem. If an artist does want their image removed they can either contact myself of Wikia and it can be easily removed.
As for gathering images: Uploading images that won't be used on any pages don't really serve a purpose.... That being said, if you would like to start a collection (on a blog post or perhaps on the forums)that would be fine.