I don't think we should do this. A great thing about our "contest" is that it isn't really a contest or competition. It's just a fun way to share our pictures, and it was originally designed to do that in meta.
I like that we can post what we want without it being judged. There are no winners or losers.
In reality, the photo with the most votes isn't the "best" picture, and the photo with the fewest number of votes isn't the "worst" picture. The pictures voted in between aren't any more or less interesting than the rest.
If we turn this into something that has a prize, especially a featured spot on the main site for a month, it would change the focus (no pun intended!). I wouldn't post or vote, because I wouldn't want to have any responsibility for the outcome. Having spoken to a few others, I'm not alone.
The contests are already featured on the main page, with a link to the current month's activity, and I think that's a great way to increase viewing and participating.
Other than that, I think we should leave this how it started, with everyone just having a good time seeing where people have been, or what they've done.