.. made some good points.
The school raised it with the police, and they are duty bound to record the 'offence'. However, that is no guarantee it would ever surface again. In the future, if young man decides to go for a job in public service - a policeman, teacher, lollypop man, chat show host - whatever, then the process would be:
Potential employer would ask for a Criminal Records Bureau check. Check would come back positive, at which point the police have the right to decide it was too long ago, too trivial etc and can ignore the finding. Second, they would contact the young man and tell him that they have received a request, and that the CRB check has turned something up.
Young man then has the option to challenge the CRB check, and it may at that point go no further. Only if those two hurdles are tripped over would the result return to the potential employer, who themselves might decide it is all bollocks and ignore it.
Who is at fault here? The boy for doing something childish? Hardly. Apart from the inconvenience of a few photons, it is unlikely to be a novel picture that causes a particular offence. The girl for doing something irresponsible as well? Dubious, really. Even if she forwarded it with a bit of libellous writing attached, hardly the crime of the century. The fault surely lay with the teacher for propagating the pain, and not dealing with it sensibly in loco parentis.