It's hard for me to imagine that f.DS could get permission to make avatars out of the actual Dominion art yet not be allowed to do so from the Iso art. It's not like it's my decision to make, I just can't imagine a plausible reason.
I can think of a reason! The actual Dominion art is all owned by one entity - RGG. The isotropic art, which again is in most cases simply the art I used in my prototypes, is just random googled images from a variety of sources, with a variety of owners. Witch is from The Wizard of Oz, someone owns that; maybe not the same entity that owns the Princess Bride image on Scheme, or the Popeye image on Sea Hag, or the Magic card art on Cutpurse, etc. etc.
At the same time, if you really like that painting of Napoleon on Tactician, or the Red Sea fort shown on Outpost, or the Conan painting on Adventurer, etc. etc., you can google those things yourself and find them. Try an image search on the name of the card, then try adding "castle" or "medieval" or "painting," although when you add medieval you will get some ugly porn, lemme tell you. Of course if you have the isotropic image handy you can also google the image directly and maybe find bigger versions. I just did this for that little copy of Highway's image that appears just above us in this thread, and immediately got multiple copies of the original source image.
http://m.cdn.blog.hu/si/sikeresvaros/image/Via%20Appia.jpg