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?
26 Aug - Question on meta, "What should September's contest theme be?"
1 Sep - Question on main, "September's contest. Theme is xyz."
And if someone else tries opening their own questions outside of this plan, moderators step in.