Are you over 18? A snapshot of current age verification mechanisms

There are many online spaces that children should not enter to shield them from adult content, services and products. Age verification mechanisms are used to bar entry to minors. We examine the arguments for and against their use, and propose three dimensions that these kinds of mechanisms ought to judged by: (1) effectiveness \& inclusivity, (2) affordability, and (3) privacy preservation. We used a systematic literature review to provide a snapshot of age verification practice in the research literature and commercial arena. We found a wide range of age verification mechanisms, ranging from "verification theatre" (box checking to confirm adulthood) to those that verify age by confirming identity. The latter elicit significant security and privacy concerns while the former clearly constitute no obstacle at all. Some mechanisms use facial biometrics to estimate age (for a fee), but the costs can easily become prohibitive for small businesses. We suggest directions for future research into solutions that can provide a more effective and affordable solution, which crucially also respect the privacy of users.