The feeling of being watched makes people act more honestly, even if the eyes are not real, a study suggests.
A Newcastle University team monitored how much money people put in a canteen "honesty box" when buying a drink.
They found people put nearly three times as much in when a poster of a pair of eyes was put above the box than when the poster showed flowers.
The brain responds to images of eyes and faces and the poster may have given the feeling of being watched, they say.
Writing in the journal Biology Letters, the team says the findings could aid anti-social behaviour initiatives.
The experiment made use of a long-running honesty box scheme based in a canteen at Newcastle University.
Over the course of 10 weeks, an A5 poster listing hot drink prices was placed at eye-level above the honesty box.
Each week, the poster featured different images of either flowers or a pair of eyes looking directly at the observer.
At the end of every week, the team calculated the total amount of money collected and the amount of drink likely to have been consumed.
Dr Melissa Bateson, a behavioural biologist from Newcastle University and the lead author of the study, said: "We found that people paid 2.76 times as much money when we put a notice on the wall that featured a pair of eyes as opposed to when the image was of some flowers."
She believes this happens because the eyes on the poster may affect people's perception that they are being watched by other people.
"Although it was just a photocopied black and white poster, we know that people's brains are set up to process faces and eyes, and that is probably because it is very important for us to know if we are being watched by other people."
The scientists believe their findings may have applications in initiatives to curb anti-social behaviour or for law enforcement.
"It does raise the possibility that you could get people to behave more co-operatively or pro-socially by putting up pictures of eyes," said Dr Bateson.
"It would work particularly in instances where people have to make a choice between whether to behave well or badly."
She said CCTV or speed cameras might be a possible application.
Professor George Fieldman, an evolutionary psychologist from Buckinghamshire Chilterns University College, said: "This paper beautifully demonstrates that people behave better when being watched.
"It would be interesting to know how one can apply these sorts of findings more generally in organisational structures and in society in general to maximise upon honourable and altruistic behaviour."