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.