Decades ago, I came up with 'micro-kerning' - an added single length gap added to few scattered letters = unique message for each person you send it to. True, y

Decades ago, I came up with 'micro-kerning' - an added single length gap added to few scattered letters = unique message for each person you send it to. True, you have to keep an index to compare to ID the leaker. Various governments used to do this for this reason in the last few years of the 1980's. Smart people used to copy/paste with a constant width font to defeat this. Then locked pdf helped, but OCR got around this. I think you can use steganographic encoding of scattered dots in a jpg, which laser printer catch money copiers with these days. The dots can be found with a scanner and again needs an index to 'read' the color photo. I have a friend who was an ambassador until he retired = I will ask, but he might consider it sensitive, and not reveal it - likely?