I thought it might be helpful for some of your artists to know they can edit their images online at Picnik, a great site that's free. There's no need for any software and they can crop, resize (yes, image some of them finally learning how to resize!), adjust and use filters. No need for Photoshop–all they have to be able to do is upload the file and then download it when they're done.
It's really a lot of fun and even Time magazine recommended it as an alternative to Photoshop in their recent article about how free software is gaining ground.
Update: Picnik joined Google in 2013 and helped with the Google photo editor, another free photo editing tool. There are so many other options online now, just a search away.