People behave more honestly and cooperatively when they feel observed — even when the sense of being watched comes from nothing more than an image of a pair of eyes. This taps into a deep, largely automatic social instinct: the feeling of being seen changes behavior regardless of whether any actual observation is happening, because the automatic System 1 response doesn't carefully verify whether a picture constitutes real surveillance before reacting to it.
The practical uses of this effect are genuinely double-edged: it can nudge people toward better behavior in shared spaces (an honesty box, a recycling area) at essentially zero cost, but it's also a reminder that a felt sense of being watched — real or manufactured — is doing real behavioral work that has nothing to do with actual moral reasoning.
In a British university office kitchen, researchers alternated the poster above a shared coffee/tea 'honesty box' — where staff were expected to leave payment on the honor system — between an image of a pair of watching eyes and an image of flowers, switching weekly. Contributions to the honesty box were roughly three times higher during the weeks the eyes poster was displayed than during the weeks the flowers poster was up, even though nothing else about the setup changed and no one was actually monitoring who paid what.