That's all you have to do. Comment, post picks, maybe submit some links or pictures or something that people can and will be a fan of. Make them different from the ones already posted though, or no one will bother to look at them. Keep at it and the medal will be your reward.
But you know, you really shouldn't be contributing just because you want a medal. You should be doing it because it's fun, and you want to. The medals are supposed to be something that you just get along the way.
