Games ... only one button to participate !!

Waouhh my requests sounds like a very crazy thing but I ask ...

Actually on my site, people with games can win cinema or concerts places (about 200 / 300 per month ...) and the only thing is to go to its profil, put its photo + name and the first who answer with "ME" are won.

I would like, like polls in fact, people only check one button to participate to a game. Like poll, the admin (or mod) chooses an option to assign a game to a post (or a forum ?) ...

when the button is checked, verification of existence of avatar/photo + field name > if yes, they are OK (but not win !!!), if not, it prevents the user from participating ...

The game must have an end (for example : my game begins 23th, and finishes the 27) ... 27 > Checked buttons disappear, and we can have with a button (dhtml ? maybe) the list of the participants : after : admin / mod checked who is the winners and publish the list.