The boy was excluded by governors after a member of staff caught him labelling the photo "tits". But the school was forced to readmit him after its decision was overturned by an independent appeals panel.
Members of the NASUWT and the Association of Teachers and Lecturers at St Cuthbert's boys' school, Newcastle, then voted overwhelmingly to refuse to teach, supervise or set work for him. The National Union of Teachers is expected to announce the result of its ballot next week.
Union members warned that the incident highlighted the increasing problem of pupils misusing camera phones in schools. They praised Gerard Murphy, the head, saying he had been put in an impossible position by the appeals panel.
Mick Lyons, NASUWT executive member, said: "We are supporting the teacher and the governing body which made the decision to exclude the boy. We find it strange that an unelected quango can overturn a decision by the governing body, who represent local people."
Mary Bousted, general secretary of ATL, said: "The situation at St Cuthbert's school clearly highlights how the exploitation of advances in mobile technology is threatening teachers and other educational professionals who should be protected."
Mr Murphy said: "We acknowledge the outcome of the NASUWT and the Association of Teachers and Lecturers' ballots and have made arrangements to ensure the pupil concerned is taught and supervised appropriately."
A spokeswoman for Newcastle council said the school had no evidence to support claims the boy had texted the image to classmates and that taking the picture would not necessarily have been grounds for excluding him.
She said: "The problem wasn't the photo itself, the problem was the caption put on the photograph."
Jock Percy, senior analyst at telecoms support services provider Ace-Comm, said: "More and more, we are seeing instances where children cannot be trusted to use their mobile phones appropriately.
"It is the mobile industry's duty to make available to parents the (software) tools they need to supervise their children's use of mobile phones. The technology to provide parents with these tools is available now."
DILEMMAS, FE FOCUS 6