I'm currently working on a couple of dios where I needed copyrighted prints for reference. I wrote to both artists, and got their permission to use them for my own reference. One asked that I would not try to sell, or pass it off as my own, and I agreed. Also I gave them both full credit for the original idea during the progress posts of the build, , and displayed the print with the finished build. The one dio is still a work in progress.
As for a few of my models, I have had people contact me to download them for magazine use, and what not. I feel that it is only fair to do this.
.