I'd have to support Giolon's comments on this issue, even though i'm not overly upset about the pics that get chosen for me.

The system seems to be geared along the lines of the phrase  "nothing succeeds like success". The most "popular" image gets chosen, so it gets more exposure and more people check it out, making it even more popular, and thus cementing it's place as your "most popular image". It's a vicious (or virtuous?) circle.

The downside is that a past image that is not representative of your gallery becomes your flagship image to the rest of the community. Not everyone likes to introduce themselves at a party by telling a dirty joke. Even if in the long run people love it, it may not be the first impression you want to give.

Perhaps using the "featured image" that users choose to use on their homepage would be a better way to go. There's nothing to calculate, you just copy the link. I'm not a programmer but that seems easier to do than setting up a bunch of multi-variable calculations.

The strong do as they can while the weak do as they must.