Image copyright South Wales Police Image caption Ysgol Gyfun Glantaf deputy head teacher Gareth Williams installed secret cameras in the school toilets to picture pupils

A global investigation into buying and selling child abuse images online has led to 13 arrests and 11 convictions in Wales, a BBC investigation has found.

Canadian police headed up Project Spade, which has seen eight convictions in the South Wales Police force area.

One included Cardiff's Ysgol Gyfun Glantaf deputy head teacher Gareth Williams who took secret photographs of children in the school toilets.

North Wales Police have had two convictions and Dyfed-Powys Police one.

The figures have been obtained by BBC Wales via a Freedom of Information request.

Media playback is unsupported on your device Media caption Police carried out raids in Caerphilly for a separate investigation

In 2013, the Toronto Police Service said its child exploitation investigation led to 348 arrests worldwide and the rescue of 386 children.

The figures also show 24 people have been referred to the Gwent and North Wales Police forces.

Neither Dyfed-Powys Police nor South Wales Police would say how many have been referred to them.

The conviction of Williams last year was one of the most high-profile cases to emerge from Project Spade.

Investigators found he had secretly photographed pupils at the school he worked by concealing a camera on the water cistern in the toilets. He captured images of 31 children aged between 11 and 16.

Williams admitted 31 charges including nine of voyeurism and 20 of making indecent photos.

He was jailed at Cardiff Crown Court for five years, which was later cut to four.

Image copyright Toronto Police Image caption Project Spade has so far identified criminals in over 50 countries

Background to the project:

Details about UK suspects were passed on to the Child Exploitation and Online Protection Centre (CEOP), which was absorbed into the National Crime Agency (NCA).

That information was then passed on to individual forces.

But since then, the NCA has referred itself to the Independent Police Complaints Commission (IPCC) over its own delays in relation to Project Spade, while referrals from other forces are currently being assessed by the police watchdog body.

North Wales Police's handling of its cases is also being looked at by the IPCC. The force was given the names of three possible paedophiles by the NCA but did not act on them for a year.