I honestly have no idea how to improve it. The problem seems to be that people are obviously having family and friends join PrestoPhoto to vote for them. That happens on a lot of sites contest unfortunately. The only way I have seen that avoided was on sites that the voting with done through a forum pole and if if you hadn't made at least 10 post (I think it was 10, maybe 25) on the forum to be able to vote. I have no clue how that could be done on a site contest like PrestoPhoto. We just have to hope that people will be honest in the contest. May when a contest is started in the description add a note about being fair and not asking you friends and family to join just so they can vote for you.
I know that with our little contest here even with no prizes, some have felt like people are picking winners by people that contribute more on the forum than others regardless of how deserving an image or page is of winning. You are always going to have to deal with favoritism over actual work unfortunately.