Teachers are calling for much tougher restrictions to protect staff from "cyber bullying" by pupils.
The Association of Teachers and Lecturers has warned of the distress caused to teachers by anonymous, malicious comments on websites.
"Offensive" comments and mocking video clips should not be allowed to undermine teachers' authority.
Such public attacks "belittle and bully" classroom teachers, says the teachers' union.
The union's general secretary Mary Bousted says that the public mockery of teachers "robs them of dignity and self-esteem".
Such "verbal abuse" needed to be curbed, the union says - and it is calling on the government to "take all reasonable steps to protect the integrity" of teachers.
In response, a spokesperson for the Department for Education and Skills says that: "Teachers now have stronger legal powers to deal with cyber pests as part of our continued fight against bullying.
"They can now confiscate mobile phones which are being used in a malicious or disruptive way. We encourage them to make full use of this power."
A survey quoted by the union claimed that 45% of teachers had received an attack by e-mail, 15% had received threatening texts - and that 10% had been upset by messages written about them on websites.
Andy Brown, a teacher at Ballymena Academy in Northern Ireland, told the union's annual conference in Bournemouth that staff were being harassed by anonymous insults on websites.
These included doctored images designed to ridicule teachers - and allegations or innuendo about their professional ability and personal lives.
Mr Brown described a secondary teacher who had been pushed into early retirement by a "campaign of derogatory and false statements placed on a website".
"What about teachers who've had pictures taken and posted of them when they're socialising or have had comments questioning their fidelity to their partner?" he told the conference.
Mr Brown said that he had checked comments made about himself on the RateMyTeachers website - which allows pupils to publish their opinions about their teachers.
He told the conference that he had found "two negative, hurtful comments about my teaching ability and me as a person".
And even though there were many more positive and complimentary comments - the two negative comments, made anonymously and available publicly, continued to rankle.
"I've had teachers on the phone to me in tears because of comments made about them. It would be easy to say 'don't read them', but it's difficult when we invest so much of our selves not to want to know what is being said about us," said Mr Brown.
The US-based RateMyTeachers website carries comments about individual, named teachers.
As an example of the negative comments is the description of a specific physics teacher in a secondary school in Wales as the "worst teacher in the school, needs to go back to uni".
Another teacher at the same school is criticised by a pupil because they "cannot speak English" and another as "the worst person ever" and "everyone hates her".
The RateMyTeachers website allows pupils to rate their teachers' ability and to add a comment - but it does not allow references to teachers' personal lives or appearance, or to use sexual language or name calling.
Michael Hussey, the New York-based founder of the RateMyTeachers website, rejected the ATL's criticism.
"This is absurd. RateMyTeachers has rules - we read everything before we put it on the website, no name calling, no bullying, certainly no threats.
"For them to link our site with cyber bullying is ludicrous. They are trying to discredit what we are all about."
He said 70% of the ratings on the site were positive.
"But there are bad teachers. There are teachers who do not care, there's no passion, they are there for the pay cheque.
"We want to show who is really connecting with their students and who simply doesn't care."