How to implement online warnings to prevent the use of child sexual abuse material

Online CSAM offending is a challenge for law enforcement, policymakers and child welfare organisations alike. The use of online warning messages to prevent or deter an individual when they actively search for CSAM is gaining traction as a response to some types of CSAM offending. Yet, to date, the technical question of how warning messages can be implemented, and who can implement them, has been largely unexplored. To address this, we use a case study to analyse the actions individuals and organisations within the technology, government, nongovernment and private sectors could take to implement warning messages. We find that, from a technical perspective, there is considerable opportunity to implement warning messages, although further research into efficacy and cost is needed.