There is an interesting discussion in the forums about what happens if you send an image to a friend and they publish it commercially.
“Could the sending of that email give the dive operator implicit permission or any other right to publish the photograph on their site (hosted in the USA) to promote one of their courses? … The DMCA counter-claim effectively says that they assume a right to publish because conditions weren’t expressed in the original email.”
A Wetpixel member is in the process of trying to get a photo removed from a dive operator’s website. The dive operator says that they have permission to use it because there were no conditions attached to the email.