Doni Scheindlin , Sep 20, 1998; 11:49 a.m.
A copyright symbol or the word copyright with your name and the year(optional). You could also put "all rights reserved" as an added reminder. I also include a phone number so whoever has the photo can contact me. Any photo lab, printer, etc., should honor the copyright. I don't know if this means that they all do, but I know that the professional labs I deal with are very clear about it.