Tracing child abusers: Where was this picture taken?

Europol holds more than 40 million images of child sexual abuse but often it doesn't know who the abusers or victims are.

So it's posting parts of these images online - with the people removed - and asking the public to help identify the locations.

A film by Lily Freeston and Sam Judah for BBC World Hacks. Find out more on the podcast.