This begins and ends with the fact that if you can see something, you can record it. The only way to prevent this is through on-site access only with a thorough

This begins and ends with the fact that if you can see something, you can record it. The only way to prevent this is through on-site access only with a thorough physical search and no electrical devices allowed. You can do some clever things to figure out who it is that leaks stuff, but that's another issue.