Hi
I believe it is everybody's right to do what they feel is best for their child. I have only recently become a dad of the most beautifull litlle girl and understand the feelings a parent has for their children. It is your first and utmost responsibility to protect them.
This being said, you cannot wrap them up in cotton wool and deprive them of this world. Assess the situation and see the risk involved. I look at your sitaution as follows.
1. All Schools do it and therefore you have a very limited if any choice of schools who dont put their photos on the internet. This is also most probably the way you found your childs school in this day and age.
2. If you remove your childs photo and the other kids photos are still up, you dont remove your child from the potential harm. As a comment posted earlier, organisied pheadophile rings
(That just sounds sick) target groups and schools so you will most likely have them watching schools etc. You cannot avoid your child playing outside.
3. You as a parent also has a duty to equip your child socially so think of what it will do to that child later on when you deprive him of the basics other kids are allowed to enjoy. They will only rebel when the get older. Rather teach them from young about responsibile behaviour.
It is tough but rather use your energy to implement training of staff etc to be on the lookout for the physco's that want to harm our little treasures.