I've just been reading this question, and I have a suggestion for a compromise for having photo contests on this site.
I think having everyone open their own contest questions would be bad thing, for the same reasons others have given. What about instead, having just one every calendar month?
For example...
26 Aug - Question on meta, "What should September's contest theme be?"
1 Sep - Question on main, "September's contest. Theme is xyz."
etc...
And if someone else tries opening their own questions outside of this plan, moderators step in.
Your thoughts?