Yes, all DRM systems are inherently impossible to make fully secure with only local data. However, several other options exist: * Needing to contact an extern

Yes, all DRM systems are inherently impossible to make fully secure with only local data. However, several other options exist: * Needing to contact an external server to view an image (of course, you could always take the opportunity to save the now-viewable image then share it) * Charging a large fee / legal contracts for the information on how to decode (security through obscurity) * Making circumvention illegal and enforcing this with fines or jail time. This is probably the only option that "actually works" as you've turned the technical problem into a social problem. People would still break it, but you could simply arrest them if they try to help others do the same.