I hadn't thought much past the "who wants a contest?" part. Let's see if I can think on my feet after interpreting a CNA class all day. There's more than a little oatmeal between the ears right now.
The theme would be whatever holiday is upcoming. Since Halloween is first up, that would be the first theme. Whatever you think of when you think of Halloween. The only rules would be to make sure everything you use can be used legally. Since it will have to come from an album to be used on the homepage, it will be automatically sized to 600 on the longer side if you go above that in the making of it when you upload it. As for the judging, why can't everyone judge? Just don't vote for your pic.
Any other suggestions? Did I forget something?