To vote, click the contest category or individual photo that interests you the most then click the plus sign (+) to vote it as your favorite for that category. Remember that you can only have 1 favorite for each category.
To change your vote, click the picture that you selected as your favorite and click the minus sign (-) to de-select that image as your favorite. You are now free to select a different photo as your favorite in that category.
Visit the Current Favorites page to view the photos that you have selected as your favorites and to rank them as the overall best.