What is Skins.be policy about pictures/wallpapers produced on this site being posted to other wallpaper websites?

I've emailed this site through the http://www.skins.be/contact/ link and received no reply, so I don't know if this is a matter of concern or not. If it is not, then I will leave it alone. But I have found some websites that have wallpapers that are clearly tagged Skins.be (in the lower right corner) that people have uploaded as their own work, without giving credit to Skins.be. I have also encountered some wallpapers that are clearly from Skins.be but have been cropped (poorly) to remove the area of the tag (i.e., 1279x971 aspect resolution).

What should I do when I find these things?