"There are choices. In our area, you do not have to pay for the sitting or photo from the school selected photographer to have the picture in the yearbook. If pictures are wanted for personal use, you pay for them, but no one is required to do so to have it appear in the yearbook. In fact, if you don't like the way the first one turned out, you can even have it re-done by the same photographer at no cost. Still, you're not required to buy any of them or pay for the service. Secondly, as far as I know, no one is forced to buy the yearbook in the first place."
Do those who pay the school tax have the choice of subtracting the cost of the school photographer from their tax bill?
Bring it up to the school board. Elect people to the school board who vow to get rid of the school photographer if you feel that strongly about it. Run for school board yourself. Personally, I have bigger worries than the school selected photographer, but to each his own.