People are better behaved when they have a sense of "Big Brother" watching them, research has shown.
Psychologists found that cafe diners were less likely to leave tables untidy when surrounded by posters of staring human faces.
When pictures of flowers decorated the walls, more empty plates and litter were left to be cleared away.
The same researchers from the University of Newcastle previously found that images of eyes prompted contributions to an honesty box in a tea room.
They believe the findings have implications for combating anti-social behaviour.
Study leader Dr Melissa Bateson, from the university's Centre for Behaviour and Evolution, said: "These findings reinforce the conclusion from our previous research, that the presence of eye images can encourage co-operative behaviour.
"We think that the images of eyes work by making people feel watched.
"We care what other people think about us, and hence we behave better when we feel we are being observed."
Dr Bateson added: "We found that the impact of the posters was a lot greater at times when the cafe was quiet.
"This makes total sense, because we would expect real people to have the greatest effect on the feeling of being watched and hence swamp the effect of the posters during busy times."
The research is based on the theory of "nudge psychology" which suggests people can be subtlety coaxed into doing the right thing without feeling forced.
Dr Bateson added: "This study confirms that the display of images of eyes has broad potential as a 'nudge', not just because eyes grab attention, but because of more fundamental connections between the feeling of being watched and co-operative behaviour.
"Even painting a pair of eyes on a wall may be useful for preventing anti-social behaviour in quiet locations."