A supply teacher has admitted a string of child sex offences after taking more than 100 secret photographs up teenage girls' skirts while working at multiple schools.Abusali Rahman, 36, who taught English, was arrested after a parent contacted police over an image of their child in school uniform being circulated on social media.Following an investigation into upskirting and voyeurism, officers identified 13 girls aged between 13 and 16 at seven high schools across Greater Manchester who were allegedly targeted by Rahman over an 18-month period.In all the identified cases, their schools – in Bury, Bolton and Salford - and parents have been informed.But police are urgently trying to trace four girls from two high schools whose pictures were found following Rahman's arrest but who have not yet been identified.The former teacher pleaded guilty to 21 child sex offences when he appeared via video link at Bolton Crown Court.Recorder Geoffrey Lowe adjourned sentencing until September 1 to await a psychiatric report.Rahman's defence barrister Emma Kehoe said: 'He was going through a mental health crisis at the time.' Officers identified 13 girls aged between 13 and 16 at seven high schools across Greater Manchester who were allegedly targeted by Abusali RahmanRahman, described by police as a British national of Bangladeshi ethnicity from Salford, became a qualified teacher in 2023.There are twelve counts of taking an indecent photograph or pseudo-photograph of a child by upskirting.Four counts of publishing an obscene article involving AI-generated sexualised images.Three counts of making an indecent photograph or pseudo-photograph of a child involving making AI-generated images.One count of distributing an indecent photograph or pseudo-photograph of a child by sharing an upskirting image with another user.One count of operating equipment beneath clothing of another without consent.Rahman was arrested in June 2025 after a concern was raised by a parent about an image of their child in school uniform being circulated by a social media account.It prompted an upskirting investigation by Greater Manchester Police's Online Child Abuse Investigation Team.Since then, a significant amount of specialist and sensitive work has since gone into trying to identify girls on those images, police have said. The former teacher pleaded guilty to 21 child sex offences when he appeared via video link at Bolton Crown CourtThe offences are alleged to have taken place between December 2023 and June 2025.All the upskirting charges relate to alleged offending in schools.Safeguarding teams are involved, with specialist support on offer.Greater Manchester Police said all schools where Rahman worked have been contacted.Speaking outside court, Detective Sergeant Simon France said: 'Protecting children is our highest priority.'All parents and guardians of those affected and their schools have been made aware of our investigation.'He added: 'We have been in contact with all the schools where Rahman has worked.'No further criminal offences have been identified.'Detective Chief Superintendent Rebecca McKendrick, head of GMP's Public Protection Division, said our 'team has painstakingly worked through the evidence to build a case against Rahman'.She added: 'The victims have been at the forefront of our investigation, and we have kept their parents and guardians and their schools informed and supported throughout this process.'Protecting children remains our highest priority, and we will continue to work closely with and meeting the victims, schools and local authorities to ensure there is support in place for anyone affected.'Alex Mann, senior prosecutor for the Crown Prosecution Service, said: 'This was a horrifying case involving an abuse of trust that affected multiple young victims.'Rahman fell well below the standards expected of his role – first by sharing sexualised deepfake images online, before escalating to upskirting and voyeurism offences.'Following a comprehensive GMP investigation, prosecutors were able to piece together a compelling case that left the defendant with little choice but admit his crimes.'The guilty pleas entered today means he will face the consequences of his appalling actions, without victims having to prolong their suffering by reliving their experiences at trial.'Rahman hasn't worked in schools since his arrest.