Once a few pictures with low ratings get rated higher than they should, it can create a cascading effect, pulling up other pictures that have beat them. It's a pretty tough problem to fix other than just giving the problem causing pictures more battles and letting it figure out that they are too highly rated. That said, if I have examples of pictures that are out of wack, I can force them into the rating queue to help resolve it....
The girls are probably better just because they tend to get a lot more votes