I'm a traditional artist, so I will probably choose that kind of pictures I think it may prove useful for traditional artists as a reference. Anyway, you are allowed to use them in any way you want, for photomanipulation etc.
My rules are simple:
1. Credit me in the description. You may use my pictures off DA, just credit me. Thanks.
2. Do not claim my photos as yours.
3. Let me know where you used my photos, as I am terribly curious. Preferably through note or comment on the picture or on the main page.
4. You can use my stock for DA prints and other commercial purposes.
5. Have fun
Feel free to check my main account: siluan.deviantart.com
Or my website: www.siluan.cz
Edit: I log in today and I have found out one of my pictures received a DD! That's so great! Thanks for the support I hope you will find my stock useful!