Nowadays it's commonplace to filter images, remove red eyes, touch up blemishes and airbrush away kilograms. But people were tampering with photos long before Photoshop came along.

Since photographers could take photos they've played around with them. Fourandsix Technologies has been looking at the most controversial and notorious photos tampered with throughout history. Tinkered images include Abe Lincoln's head being popped on another politician's body, Hitler removing one-time right-hand-man Joseph Goebbels and Stalin airbrushing out his former-friends-turned-enemies.

Led by computer scientists Kevin Connor and Hany Farid, the Fourandsix team determines the image origin, its edited history, authenticity and other sneaky details you can't pick up with the naked eye. They've also created software that works out to what degree the original has been altered, which will hopefully help to highlight the biggest culprits of image manipulation and expose excessive digitalisation.