People can detect a fake image of a real-world scene only 60 per cent of the time, say scientists who suggest this may have implications for the spread of fake news.
Even when people detect a fake image, they can only tell what is wrong with the image about 45 per cent of the time, researchers found.
They set up an online test that used a bank of 40 images created from 10 original images sourced from Google Images.
Six of the original images were subjected to five different types of manipulation, including physically implausible and physically plausible manipulations, to create 30 manipulated images.
About 707 participants were shown 10 random images that included each of the five manipulation types and five original images.
Researchers found that 60 per cent of images were correctly identified as being manipulated, which was just over the chance performance of 50 per cent.
Of the people who identified a fake image, only 45 per cent of manipulations could be correctly located in the image when a grid overlay was placed on the image and participants were prompted to select the regions where a manipulation was present.
"Our study found that although people performed better than chance at detecting and locating image manipulations, they are far from perfect," said Sophie Nightingale, PhD student at University of Warwick in the UK.
"This has serious implications because of the high-level of images, and possibly fake images, that people are exposed to on a daily basis through social networking sites, the internet and the media," Nightingale added.
In a second experiment using an image set created by the authors, 659 people completed an online task that tested their ability to locate manipulations regardless of whether or not they said there was one present.
The results revealed that ability to detect something wrong was similar (mean 65 per cent of the time) to the first experiment but that manipulations were accurately located in the image 39 per cent more of the time than expected by chance.
This suggests that people are better at the more direct task of locating manipulations than the more generic one of detecting if a photo has been manipulated or not, researchers said.
"We found that people were better at detecting physically implausible manipulations but not any better at locating these manipulations," said Derrick Watson from University of Warwick.
So even though people are able to detect something is wrong they can't reliably identify what exactly is wrong with the image, researchers said.
"Images have a powerful influence on our memories so if people can't differentiate between real and fake details in photos, manipulations could frequently alter what we believe and remember," Watson said.
The study was published in the journal Cognitive Research: Principles and Implications.
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