It is now well documented that individuals, on average, change their behavior when their actions are observed by others. Yet, there is no systematic way of measuring this dimension of preferences at the individual level. In this paper, we propose a novel experimental game to measure the individual sensitivity to image concerns. We show that few socio-economic characteristics can explain the level of image concern. One exception is that members of ethnic minorities seem to be more imaged concerned, in particular when observed by a member of other groups. Men (resp. women) are more image concerned when observed by women (resp. men). Finally, we show that more image concerned individuals tend to be more selfish and find evidence consistent with the fact that they try to avoid situations where their actions risk being visible.