If you use photos I've taken, you...
...MUST
- credit me.
Why? I don't like if someone steals my work, whether it is photos or drawn stuff. Do you?
- post me a link to your artwork.
Why? I'm curious. And if someone has created something fantastic using a photo I've taken, it will be an honour to me, so I want to see it.
...MAY
- use my pics in your artwork; you may edit them as much as you like!
- use my pics also outside DA, if you follow all of the other rules.
...DO NOT
- use my pics in commercial purposes.
Why? 1) The quality is NOT that good. 2) If I'm not getting money out of it, no one else - company, charity... What ever! - will. I also support no political, global or religious agenda/ideology, neither do my pictures.
- claim that the pics are yours. This, I think, needs no explanation.
- use or try to use photos that aren't in stock folder.
Why? Just don't. Otherwise I'll come and eat your head...

- use any of my drawn work (traditional or digital)
Why? Because I tell you not to.
Edit: CONTESTS!
Rules for using my stocks in contests with cash involved.
Contests outside dA: No. (I've unfortunately seen too many, that don't go as they should and artists end up with 50$ or even nothing, while "the little text" in the contest rules gives contest holder all rights for use of works entered.)
Contests in/through dA: Yes, as long as using means other than just fixing the colours and things like that. If you have to compare your work for a while with the original stock to see that said image has been used OR if it is just a backround (still do something to it!), it is okey with me.