Ann Hughes, the headmistress of a school in Anglesey, North Wales, found out some children were planning to "spoil" the picture and telephoned police, a professional conduct hearing was told.
It is alleged that an officer was invited into the village primary school to reprimand the pupils unwilling to pose correctly, The Mirror reported.
Hughes faces a catalogue of complaints including repeatedly calling one student "stupid" and favouring children whose first language was Welsh.
The committee of the General Teaching Council for Wales heard yesterday that she failed to investigate the bullying of two pupils, shouted excessively in the classroom and unnecessarily criticised children's mistakes.
One pupil watched as Hughes tore his examination paper in front of him when he had spelt his middle name wrong, the hearing was told.
The school was engulfed in crisis in May 2011 when five of the six teachers simultaneously called in sick after earlier threatening industrial action following a vote of no confidence in Hughes.
Staff claimed there was a climate of "fear" at the school before the headmistress was suspended in July 2011 and later dismissed. The case is still continuing