The best advice I can give is just to document the situation for yourself, save a copy of the photo for yourself, and if you want other advice, get the school lawyer to chat with you about the matter.
We have the first amendment, and I am unaware of any criminal offense that might otherwise apply.
You can contact me at my office at 770-744-4211 or by email through this website. The questioner and any reader do not have an attorney-client relationship formed by our communications on this website. Advice given by me on this website is general advice based on partial information. You should not rely on any advice given without first hiring a lawyer in the area where the case is pending, and providing that lawyer with full information.