12 year old with inappropriate pictures on cell phone

[speck]

My son is 12 years old, had his cell phone out on the bus, which is not allowed. He was not taking pictures or talking on the phone he was recording the other kids making noises with balloons. The bus driver confiscated the phone and turned it into the person in charge at the station. This person had no reason to open the phone and look at personal information; however, she did. She saw that he had an inappropriate picture on the phone wall paper. They won't return the phone and said they are investigating it with their attorney. Are they allowed to open the phone and look at personal information, when there was no probable cause? I am not sure what category this is under so I posted it in this one as well as another.

by law yes, before the school year starts parents are required with their children to sign a bunch of papers, in those papers is a contract, stating that the school may confiscate and look into what was confiscated, depending on what the picture is/was of, the District not the school may be allowed to take Legal Action.