Honestly, I dunno. Most of the pics were made specifically for the mood theme, and permissions were not obtained for them to be used otherwise. A few were gifts to other people who allowed us to use their gifts for the mood theme, while others were pieces that artists didn't mind being used for anything.
Your best bet is to visit the links from the mood theme page back to the original art pieces and exploring whether the artist allows their work for iconing or not (using gifts is a no-no, though - you'd have to ask the giftee). If there's no clear permission (usually found on profile pages or info pages on the artist's web site), you can ask the artist directly.
If you know which pieces you want for iconing, I might know off the top of my head whether the artist allows iconing or not, so feel free to ask.