Yes, I believe that photos in a yearbook should be spread evenly between all students, because a school yearbook should show the student experience as much as possible. The student experience is varied. There is no student that deserves to be remembered more than another. A student is not worth forgetting just because he cannot make the basketball team.
I think the people who want to be shown in yearbooks do the things that will get them noticed and those who do not care or do not want attention do not. I think a class should be represented based on the activities of the people in the class. A person who participated in 10 activities should have more yearbook coverage than those who do none.
How active a student is dictates the number of photos that are placed in a yearbook. How are you going to have an even amount of photos between someone that is in sports and joins four different after school clubs compared to someone that is in band and does not join any clubs? The only way that there would be an even number of photos is if there were no extra photos included for extracurricular activities.
Its a yearbook, in time it will mean nothing to you. Times change and something as simple as a yearbook isn't going to be an issue ten years from now. The best thing you can do is just roll with the punches. It's just a thing in the past, who cares about who has more pictures.
No photos in a yearbook should not be spread evenly between all students. The editors of the school's yearbook should have artistic license to select, use and place photos as they deem in the best interest of the publication. In reality it would be impossible to spread the photos out since not all students are involved in school activites.