Ah, that link to the HD version from the steam exchange website is perfectly fine.
As for sharing the images with Nifflas or Violane's permission. Violane, as artist always has rights over her images unless she signed a document on which she gives away all her rights. I'm fairly sure she didn't and I'm also fairly sure steam does not have an agreement like that either. So if Nifflas and Violane are okay with it to host a 2nd version, thats perfectly fine. But given that steam exchange already hosts this, it may already be solved?