History is full of manipulated images. Adolf Hitler, Joseph Stalin and China Communist Party founder Mao Zedong all famously cut former allies out of historic photos after a disagreement.
Even Winston Churchill wasn’t above tampering with photographs when it suited him.
Back then, you needed special technical equipment and time-consuming darkroom techniques to manipulate an image. But since photos went digital, it has become a lot easier to modify them, and much harder to tell when an image has been tampered with.
But a Czech startup has created a product that can do just that, and banks and insurance companies are using it to detect fraud.
Back in 2004, a group of scientists and digital experts led by Babak Mahdian came together in Prague with one goal -- to build a toolkit that could instantly detect when an image has been tampered with.
Winston Churchill's cigar was removed from this image after smoking was deemed unhealthy.
They had heard fake ID's were being submitted to banks so people could create fraudulent accounts online, and manipulated images were being used to trick insurance firms.
Senior leader of the Chinese Communist Party Bo Gu was removed from this photograph after having a falling out with founding father of the People's Republic of China, Mao Zedong.
The team created Verifeyed, which uses machine learning to figure out whether photos have been through editing software, and can establish which camera or phone was used to take them.
Adolf Hitler had Joseph Goebbels (second from right) removed from the original picture after he fell out with him.
Traditional digital cameras have several components: an optical system, then a photo sensor, and finally a storage system. Each component has a unique 'fingerprint.'
A fraudster tried to trick an insurance company by making it look like a car had been damaged. This is the sort of image Verifeyed works with.
This 'fingerprint' can be unique to a camera or camera model, and can be corrupted when an image has been tampered with.
Russian dictator Josef Stalin routinely air-brushed his enemies out of photographs. In this snap a commissar was removed from the original photograph after falling out with him.
One of the ways Verifeyed spots fake images is by finding out how many times an image has been compressed into a JPEG file format for storage.
King George VI was removed from the original photograph of himself, Queen Elizabeth and Canadian Prime Minister William Lyon Mackenzie King because the PM wanted to paint himself in a more powerful light.
If an image has been tampered with, it is decompressed, loaded onto photo-editing software, manipulated, and recompressed.
Italian dictator Benito Mussolini had the horse handler removed from the original photograph so he appeared more heroic.
JPEG is a 'lossy' file format, which means that that every time you compress a JPEG image, some information is lost in order to make a smaller file.
Don't worry, Sandra Bullock is fine. This image is a fake.
When a JPEG image is compressed, it is split into adjacent blocks of pixels. Those blocks are compressed separately, but still have to relate to one another in the same way they would in the original image.
Saudi-owned English news website Al-Arabiya published a photo in which fighter jets were digitally inserted above Libyan rebel fighters near a checkpoint on the outskirts of Ras Lanuf in the north of the country.
If someone has made changes to parts of the image, they won't relate to each other in the same way. The Verifeyed algorithm is able to spot these differences.
The French Magazine Paris Match altered a photograph of President Nicolas Sarkozy by removing some body fat. The magazine said it had tried adjusting the lighting on the picture.
Once they had created the product, Verifeyed took on contracts with a bank, a media agency and two insurance firms.
The official Iranian news agency released a photo touting the country's development of a sophisticated new drone, but they had actually removed features from a picture of a drone developed by Chiba University in Japan.
After six months reviewing over 1.5 million images, about 2% of the images Verifeyed flagged were false positives -- real photos incorrectly flagged as fake.
Now that isn't a larger percentage. But if an insurance company received 4 million digital images annually, that would mean 80,000 false alarms. A lot of customers could be falsely accused of fraud.
A Russian newspaper distributed by a pro-Kremlin group printed a manipulated image supposedly showing blogger/activist Aleksei Navalny standing beside Boris A. Berezovsky (left), an exiled financier sought by Russian police.
And the Verifeyed product took one or two seconds to process each photo. A company can have thousands of photos to get through daily, so the process took too long.
A photo of Sarah Palin was went viral shortly after Palin was announced as the vice presidential nominee for the Republican ticket, depicting her in a patriotic bikini holding a rifle. It was actually a composite of Palin's head, and somebody else's body. CNN believed it was real for a time.
The team went back to the drawing board. Verifeyed's clients wanted a system that wasn't too slow or too sensitive.
Orthodox Israeli newspaper Yated Neeman digitally removed two female Cabinet members from a photo of Prime Minister Benjamin Netanyahu (centre left) and President Shimon Peres (centre right), replacing the females with male Cabinet members.
After some improvements, only 0.1% of the digital images Verifeyed examines are false positives, and it gets through images in less than a second.
Verifeyed is also used in military intelligence. The programme found that a soldier had been removed from this image.
Verifeyed, which now has nine people in its team, would not disclose its revenues to us. Mahdian also says the company has not raised any venture capital funding.
A tourist standing on a balcony on one of the twin towers was not there on 09/11/2001. The timestamp and plane were added later.
Instead, Mahdian says, Verifeyed has relied on a few business angels, but would not tell us who or how much it received. It also uses the resources of its parent company, a computer vision development firm called ImageMetry
Verifeyed CEO Babak Mahdian and CTO Radim Nedbal, pictured with Michael Bloomberg, won the NYC Next Idea competition in 2011.